Myoglobin Blooming Agent Containing Shrink Films, Packages and Methods for Packaging

ABSTRACT

Heat shrinkable, oxygen barrier, packaging films, methods of packaging and packages are provided having a myoglobin blooming agent to provide, promote, enhance or maintain a desirable coloration on the surface of a myoglobin-containing meat product.

RELATED APPLICATIONS

This is a divisional application of U.S. patent application Ser. No.11/413,504 filed on Apr. 28, 2006 which is a continuation-in-part ofInternational Application PCT/US2005/011387, with an internationalfiling date of Apr. 4, 2005, published in English as WO 2005/097486 onOct. 20, 2005, entitled “Improved Packaging Method that Causes andMaintains the Preferred Red Color of Fresh Meat,” by Curwood, Inc.,which are both incorporated herein by reference in their entireties.

TECHNICAL FIELD

Heat-shrinkable single and multilayer food packaging films, and foodpackages comprising the same, for maintaining desirable food color areprovided herein, as well as related methods of food packaging.

BACKGROUND

Meat color is an important quality characteristic of meat that affectsits merchandizability. Consumers often use color as an indicator of meatquality and freshness. The color of meat is related to the amount andchemical state of myoglobin in the meat. Myoglobin is present in themuscle tissue of all animals and functions to store and deliver oxygenby reversibly binding molecular oxygen, thereby creating anintracellular source of oxygen for the mitochondria. Pork and poultrytypically contain lower amounts of myoglobin than beef and thus arelighter in color than beef.

Myoglobin includes an open binding site called heme that can bindcertain small molecules, such as molecular oxygen (O₂ or “oxygen”), orwater. Myoglobin without a molecule bound to the heme site is a purplecolored molecule called deoxymoglobin. The presence and type of ligandbound at the myoglobin binding site can alter the color of themyoglobin. The color of the meat product will change based on the amountof myoglobin present and the amount and type(s) of ligand molecule(s)bound to the heme binding site. Molecular oxygen, O₂ (“oxygen”) readilyacts as a ligand that binds to the heme group, permitting biologicaltransport of oxygen from the blood stream to the mitochondria withincells. When oxygen binds to the heme pocket, purple deoxymyoglobinbecomes oxymyoglobin, characterized by a red color. When a watermolecule binds to the heme group, the myoglobin molecule turns brown andis referred to as metmyoglobin. The binding of cyanide or fluorine tothe heme site can cause a brown color, while the binding of carbonmonoxide (CO) can cause a red color similar to that produced by oxygenbinding. Nitric oxide (NO) has been described as forming a stable pinkcolor in cured meat.

Historically, fresh meat products available to consumers have beensubstantially prepared and packaged for end-use at the site of finalsale. Product packaging that preserves desirable color of fresh meat canpromote the merchantability and appeal of the meat product forconsumers. Existing meat packaging technology can inadequately preservefavorable meat color for various reasons. The conventional packagingformat used by the retail grocer for fresh meat is to stretch a thinplastic film around a foam tray that supports the product. The film ispermeable to oxygen so that the color of the meat quickly blooms to abright red. However, the shelf life for the bright red color is onlyabout three days. Thus, this packaging format is undesirable because thecolor often becomes unacceptable before it can be displayed or sold eventhough the meat remains nutritious and healthy for consumption. As aresult, a packaging format that maintains the fresh meat color for alonger period of time has long been sought for centralized packagingoperations. Alternatively, meat has been packaged in oxygen barrier,vacuum bags, which are vacuum sealed and prevent oxygen contact with themeat until the package is opened. Vacuum sealed red meat products arenutritious, healthy and have a long shelf life, however they may resultin an undesirable purple meat color that does not bloom to a desirablered color until the meat is exposed to air. Consumer acceptance of meathaving a purple color is less than that of meat having a red color. Toprovide meat with the consumer preferred red color meat has also beenpackaged in a modified atmosphere package (“MAP”), wherein the meat ismaintained in a sealed pocket containing an atmosphere that is differentthan ambient air. For example, one such commercially acceptable MAPcontains an atmosphere enriched with oxygen (up to 80% by volume) tobetter maintain a preferred red color. One case ready MAP maintains meatin carbon dioxide, with a very low oxygen content until just beforedisplay when the meat is exposed to oxygen to cause blooming to thedesired red color. Alternatively, the meat can be contacted with a MAPhaving an atmosphere containing a small concentration of carbon monoxide(CO) (e.g. 0.4% by volume) to maintain a preferred red meat color.However, while CO-containing MAP can maintain a shelf life comparable tovacuum packaged meat, the red color induced by the presence of CO can beperceived as “unnaturally” bright red. In addition, the red colordeveloped by CO tends to extend through a significant portion of themeat product, causing a permanent “pinking” of the interior of the meatwhich may remain even after the meat has been fully cooked. The brightred CO-myoglobin complex is referred to as carboxymyoglobin. Thepresence of carbon monoxide can also disfavorably impact sales ofCO-containing MAP packages among consumers.

MAP also requires a headspace for contact of the modified atmospherewith the meat surface to effect the desired color over time. Thisrequirement for a headspace leads to increased package volume, increasedtransportation costs and storage requirements and also limits thedisplay appearance by making the product less visible due to the highside walls of the container and the gap between the film and the meatsurface.

What is needed are packaging materials that maintain a favorable meatcolor, while providing an adequate or improved shelf life and meatfreshness.

Nitrite or nitrate salts, such as sodium nitrite, are often used incuring meat, and can also affect meat color. Nitrate and nitriteadditives are generally recognized as safe for use in foods, and arecommonly known preservatives used in the curing process for productssuch as hams, lunchmeat, bologna and hot dogs. Nitrite and nitrates areused to cure and disinfect meats in the meat industry often producing astable pink to red color in the process. For example, GB 2187081Adiscloses immersion of meat in an aqueous solution of sodium chloride,polyphosphate ions and nitrite ions to preserve meat. See also McGee,“Meat”, On Food and Cooking, Rev. Ed., 2004, Chapter 3, pp. 118-178(Scribner, New York, N.Y.) which is hereby incorporated by reference.The presence of oxygen can oxidize available nitric oxide to nitritethus reducing its availability to associate with the myoglobin molecule.Packaging films have been described that comprise nitrite or nitratecompounds as a desiccant, a food preservative or as a volatile corrosioninhibitor for packaging of metal products. Anti-fungal agents includingfood preservatives such as sodium nitrite may be applied on varioustypes of packaging to preserve biodegradable packaging against prematuredeleterious attack by fungi, as disclosed in JP7-258467A. Oxygen barrierfilms for packaging food products can contain a nitrate salt as amoisture-absorbing agent within an EVOH barrier material or other layerof a multilayer film, as disclosed in JP5-140344A, and U.S. Pat. No.4,407,897 (Farrell et al.), U.S. Pat. No. 4,425,410 (Farrell et al.),U.S. Pat. No. 4,792,484 (Moritani), U.S. Pat. No. 4,929,482 (Moritani etal.), U.S. Pat. No. 4,960,639 (Oda et al.), and U.S. Pat. No. 5,153,038(Koyama et al.). Nitrate or nitrite products have also been described asbeing included in packaging films to absorb moisture e.g. to inhibitcorrosion of metal products, as disclosed in U.S. Pat. No. 2,895,270(Blaess), U.S. Pat. No. 5,715,945 (Chandler), U.S. Pat. No. 5,894,040(Foley et al.), U.S. Pat. No. 5,937,618 (Chandler), U.S. Pat. No.6,465,109 (Ohtsuka), and U.S. Pat. No. 6,942,909 (Shirrell et al.), U.S.Published Patent Application No. 2005/0019537 (Nakaishi et al.), GBPatent No. 1,048,770 (Canadian Technical Tape, Ltd.), and EP Patent Nos.EP 0 202 771 B1 (Aicello Chemical Co. Ltd.), and EP 0 662 527 B1 (CortecCorp.) and EP 1 138 478 A2 (Aicello Chemical Co. Ltd.). None of thesebarrier films teach a meat-contact portion comprising a nitrite ornitrate material adapted to maintain desirable coloration of a meatproduct.

In many packaging applications, such as vacuum packaging, heatshrinkable food packaging films are desirable. Heat shrinkable bags canbe made from heat sealable films. A typical food packaging bag, pouch orcasing can include one, two, or three sides heat sealed by the bagmanufacturer leaving one or two open sides to allow product insertion.

Shrinkable films, bags, and casings have been used to package fresh,frozen and processed meats for wholesale or retail sale and asprocessing films for cook-in applications and post-cookingpasteurization processes. Meats cured with nitrites and/or nitrates havebeen packaged in shrink films. See e.g. U.S. Pat. No. 6,815,023 (Tatarkaet al); U.S. Pat. No. 6,777,046 (Tatarka et al); U.S. Pat. No. 6,749,910(Georgelos et al); U.S. Pat. No. 5,759,648 (Idlas); U.S. Pat. No.5,472,722 (Burger); U.S. Pat. No. 5,047,253 (Juhl et al); and U.S. Pat.No. 4,391,862 (Bornstein et al).

What is needed are packaging products, such as heat-shrinkable filmsincluding a food-contact portion comprising a material adapted tomaintain or promote the desirable coloration of a myoglobin containingfood product especially fresh meat.

SUMMARY

In a first embodiment, heat shrinkable, oxygen barrier, packaging filmsare provided that comprise myoglobin blooming agent to maintain orpromote desirable coloration of a meat product. The myoglobin bloomingagent can comprise a molecule that interacts with the myoglobin presenton the surface of the meat product to produce a color change and/or tomaintain a favorable color in the meat product. Preferably, themyoglobin blooming agent is a compound that provides a nitric oxideligand for binding to myoglobin, to promote or maintain a favorable redcolor on the meat surface. Nitrate or nitrite salts are particularlypreferred myoglobin blooming agents. The food contact portion of thepackaging films preferably includes a suitable concentration of themyoglobin blooming agent to induce or preserve a desirable color on thesurface layer of a fresh meat product. The packaging films can have anysuitable structure, but it is essential that the myoglobin bloomingagent be on, or in, or able to migrate to, a food contact portion. Thepackaging films can be single layer or multilayer, and have a freeshrink at 90° C. of at least 10% in at least one direction. Preferablythe packaging films have a total free shrink at 90° C. of at least about30%, more preferably at least 40% or 60% or more. In one aspect, thepackaging films comprise a sealant layer comprising a myoglobin bloomingagent. The multilayer packaging films can further comprise an oxygenbarrier layer. The oxygen barrier layer can comprise any suitablematerial, such as EVOH or PVDC, and is preferably positioned between thefirst and second layers. For example, the oxygen barrier layer can be incontact with the sealant layer and/or another layer. In one aspect, aheat-shrinkable food packaging film can have an interior surface and anexterior surface and can include the oxygen barrier layer and a sealantlayer comprising a myoglobin blooming agent wherein the film has a freeshrink value at 90° C. of at least 10% in at least one of the machine ortransverse directions. Advantageously, at least a portion of the film istransparent to permit viewing (after packaging) of at least a portion ofa myoglobin containing food product. Preferably, the inventive packagingfilm has good optical properties such as low haze, high gloss and goodtransparency. Beneficially, the film may also bear graphics, indicia,printing, or other information.

In another embodiment, packaged food products are provided. The foodproducts are preferably provided in a case-ready configuration. The foodproduct may include a heat shrinkable film having a food contact portionwhere that film is heat shrunken around a meat product to form apackage. The food contact portion includes a suitable concentration of amyoglobin blooming agent to provide a desired coloration of the surfaceportion of the meat product in contact with the food contact portion.The meat product is preferably a meat product with a measurable watercontent, such as fresh or cured meat, and most preferably fresh, uncuredraw meat. Preferably, the packaged food product includes a meat producthaving at least about 5% by weight moisture content. Typically, freshmeat may include about 60-80% by weight water, while cured processedmeats may include about 40-80% by weight water. Typically fresh meat mayhave less than 1.0 weight % sodium chloride. Cured processed meat mayhave 2.0 wt. % to 3.5 wt. % or higher amounts of sodium chloride.Preferably, the packaged food product includes a meat product having amyoglobin concentration of at least about 0.1 mg per gram of meat orhigher concentrations up to about 25 mg/g, and optionally at least about5% moisture content. Examples of suitable fresh meat products includepoultry, fish, beef and pork. The package may have any suitableconfiguration, including vacuum packaging, or trays enclosed in a filmof the first embodiment.

In yet another embodiment, methods of packaging a myoglobin-containingfood product are provided. Shrink films may be provided in a variety ofpackaging formats using conventional packaging methods in combinationwith the above described heat shrinkable film to produce containers andpackages such as bags, pouches, casings, vacuum packaging including formshrink packaging, and tray overwraps, etc. and combinations thereof withor without modified atmosphere packaging.

Beneficially, a food product comprising myoglobin, preferably having amoisture content of at least 5 wt. %, may be provided for packaging lessthan 20 days post-mortem, preferably less than 12 days post-mortem, andmore preferably 6 days, 3 days, 2 days, 24 hours or less post-mortem.Preferably, a meat product is contacted by a packaging materialcomprising a food contact surface having a myoglobin blooming agent,which may preferably be present in an amount of between about 0.001mg/in² and about 0.900 mg/in² or which may be present on the surface inan amount of up to 10 μmoles/inch² or higher, preferably from about 0.01to 10 μmoles/inch². Use of amounts on the surface greater than 10μmoles/inch² may provide an undesirable depth of penetration and use ofamounts less than 0.01 10 μmoles/inch² may be insufficient to convertenough myoglobin to cause a visibly perceptible color change, but thiswill be dependent upon such parameters as choice of the particular typeof myoglobin containing food such as poultry versus pork versus beef andalso upon variations within a particular type such as dark cutting meatversus light cutting meat. Other parameters such as the amount ofavailable myoglobin also affect the amount of MBA needed to achieve thedesired effect. It will be appreciated that greater or lesser amountsmay be used depending upon process and other parameters chosen as longas the desired color effect is produced and the actual amount for aparticular application and parameters may be determined without undueexperimentation. It is expected that the amount most often used willtypically fall within the above range. Also preferably, the packagingmaintains the food product in a reduced oxygen package environment i.e.having a reduced gaseous oxygen partial pressure. The reduced oxygenpackage may comprise an oxygen barrier layer having an oxygentransmission rate of less than about 310 cm³/m²/24 hours measured at 0%relative humidity and 23° C. Advantageously, the package is hermeticallysealed and minimizes or eliminates oxygen transfer across the filmand/or tray thickness.

The compositions, films, packages and methods provided herein are usefulto provide packaged fresh, frozen, thawed, processed and/or cured meatproducts having a desirable surface color, such as red for fresh groundbeef.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross sectional schematic of a first exemplary multilayerfilm.

FIG. 2 shows a cross sectional schematic of a second exemplarymultilayer film.

FIG. 3 shows a cross sectional schematic of a third exemplary multilayerfilm.

FIG. 4 shows a cross sectional schematic of a fourth exemplarymultilayer film.

FIG. 5 shows a cross sectional schematic of a meat containing tray withshrink film overwrap.

FIG. 6 shows a top view of a shrink film enclosed meat cut.

FIG. 7 shows a cross sectional schematic of a meat containing formshrink container.

DETAILED DESCRIPTION Definitions

In discussing plastic film packaging, various polymer acronyms are usedherein and they are listed below. Also, in referring to blends ofpolymers a colon (:) will be used to indicate that the components to theleft and right of the colon are blended. In referring to film structure,a slash “/” will be used to indicate that components to the left andright of the slash are in different layers and the relative position ofcomponents in layers may be so indicated by use of the slash to indicatefilm layer boundaries. Acronyms commonly employed herein include:

EAA—Copolymer of ethylene with acrylic acid

EAO—Copolymers of ethylene with at least one α-olefin

EBA'Copolymer of ethylene with butyl acrylate

EEA—Copolymer of ethylene with ethyl acrylate

EMA—Copolymer of ethylene with methyl acrylate

EMAA—Copolymer of ethylene with methacrylic acid

EVA—Copolymer of ethylene with vinyl acetate

EVOH—A saponified or hydrolyzed copolymer of ethylene and vinyl acetate

PE—Polyethylene (an ethylene homopolymer and/or copolymer of a majorportion of ethylene with one or more α-olefins)

PP—Polypropylene homopolymer or copolymer

PET—Poly(ethylene terephthalate)

PVDC—Polyvinylidene chloride (also includes copolymers of vinylidenechloride, especially with vinyl chloride and/or methyl acrylate (MA)),also referred to as saran

A “core layer,” as used herein, refers to a layer positioned between andin contact with at least two other layers.

An “outer layer,” as used herein, is a relative term and need not be asurface layer.

The term “exterior layer” refers to a layer comprising the outermostsurface of a film or product.

The term “interior layer” refers to a layer comprising the innermostsurface of a film or product. For example, an interior layer forms theinterior surface of an enclosed package. The interior layer can be thefood-contact layer and/or the sealant layer.

As used herein, the term “barrier,” and the phrase “barrier layer,” asapplied to films and/or film layers, are used with reference to theability of a film or film layer to serve as a barrier to one or moregases or moisture.

The term “nanocomposite” shall mean a mixture that includes a polymer,or copolymer having dispersed therein a plurality of individualplatelets obtained from an exfoliated modified clay and having oxygenbarrier properties.

The term “adhesive layer,” or “tie layer,” refers to a layer or materialplaced on one or more layers to promote the adhesion of that layer toanother surface. Preferably, adhesive layers are positioned between twolayers of a multilayer film to maintain the two layers in positionrelative to each other and prevent undesirable delamination. In someembodiments a peelable tie layer may be used which is designed to haveeither cohesive failure or delamination from one or both adjacent layersupon application of a suitable manual force to provide an openingfeature for a package made from the film. Unless otherwise indicated, anadhesive layer can have any suitable composition that provides a desiredlevel of adhesion with the one or more surfaces in contact with theadhesive layer material. Optionally, an adhesive layer placed between afirst layer and a second layer in a multilayer film may comprisecomponents of both the first layer and the second layer to promotesimultaneous adhesion of the adhesive layer to both the first layer andthe second layer to opposite sides of the adhesive layer.

As used herein, the phrases “seal layer,” “sealing layer,” “heat seallayer,” and “sealant layer,” refer to a film layer, or layers, involvedin the sealing of the film: to itself; to another film layer of the samefilm or another film; and/or to another article which is not a film e.g.a tray. In general, the sealant layer is a surface layer i.e. anexterior or an interior layer of any suitable thickness, that providesfor the sealing of the film to itself or another layer. With respect topackages having only fin-type seals, as opposed to lap-type seals, thephrase “sealant layer” generally refers to the interior surface filmlayer of a package. The inside layer frequently can also serve as a foodcontact layer in the packaging of foods.

“Polyolefin” is used herein broadly to include polymers such aspolyethylene, ethylene-alpha olefin copolymers (EAO), polypropylene,polybutene, ethylene copolymers having a majority amount by weight ofethylene polymerized with a lesser amount of a comonomer such as vinylacetate, and other polymeric resins falling in the “olefin” familyclassification. Polyolefins may be made by a variety of processes wellknown in the art including batch and continuous processes using single,staged or sequential reactors, slurry, solution and fluidized bedprocesses and one or more catalysts including for example, heterogeneousand homogeneous systems and Ziegler, Phillips, metallocene, single siteand constrained geometry catalysts to produce polymers having differentcombinations of properties. Such polymers may be highly branched orsubstantially linear and the branching, dispersity and average molecularweight and may vary depending upon the parameters and processes chosenfor their manufacture in accordance with the teachings of the polymerarts.

“Polyethylene” is the name for a polymer whose basic structure ischaracterized by the chain —(CH₂—CH₂—)_(n). Polyethylene homopolymer isgenerally described as being a solid which has a partially amorphousphase and partially crystalline phase with a density of between 0.915 to0.970 g/cm³. The relative crystallinity of polyethylene is known toaffect its physical properties. The amorphous phase imparts flexibilityand high impact strength while the crystalline phase imparts a highsoftening temperature and rigidity.

Unsubstituted polyethylene is generally referred to as high densityhomopolymer and has a crystallinity of 70 to 90 percent with a densitybetween about 0.96 to 0.97 g/cm³. Most commercially utilizedpolyethylenes are not unsubstituted homopolymer but instead have C₂-C₈alkyl groups attached to the basic chain. These substitutedpolyethylenes are also known as branched chain polyethylenes. Also,commercially available polyethylenes frequently include othersubstituent groups produced by copolymerization. Branching with alkylgroups generally reduces crystallinity, density and melting point. Thedensity of polyethylene is recognized as being closely connected to thecrystallinity. The physical properties of commercially availablepolyethylenes are also affected by average molecular weight andmolecular weight distribution, branching length and type ofsubstituents.

People skilled in the art generally refer to several broad categories ofpolymers and copolymers as “polyethylene.” Placement of a particularpolymer into one of these categories of “polyethylene” is frequentlybased upon the density of the “polyethylene” and often by additionalreference to the process by which it was made since the process oftendetermines the degree of branching, crystallinity and density. Ingeneral, the nomenclature used is nonspecific to a compound but refersinstead to a range of compositions. This range often includes bothhomopolymers and copolymers.

For example, “high density” polyethylene (HDPE) is ordinarily used inthe art to refer to both (a) homopolymers of densities between about0.960 to 0.970 g/cm³ and (b) copolymers of ethylene and an alpha-olefin(usually 1-butene or 1-hexene) which have densities between 0.940 and0.958 g/cm³. HDPE includes polymers made with Ziegler or Phillips typecatalysts and is also said to include high molecular weight“polyethylenes.” In contrast to HDPE, whose polymer chain has somebranching, are “ultra high molecular weight polyethylenes” which areessentially unbranched specialty polymers having a much higher molecularweight than the high molecular weight HDPE.

Hereinafter, the term “polyethylene” will be used (unless indicatedotherwise) to refer to ethylene homopolymers as well as copolymers ofethylene with alpha-olefins and the term will be used without regard tothe presence or absence of substituent branch groups.

Another broad grouping of polyethylene is “high pressure, low densitypolyethylene” (LDPE). LDPE is used to denominate branched homopolymershaving densities between 0.915 and 0.930 g/cm³. LDPEs typically containlong branches off the main chain (often termed “backbone”) with alkylsubstituents of 2 to 8 carbon atoms.

Linear Low Density Polyethylene (LLDPE) are copolymers of ethylene withalpha-olefins having densities from 0.915 to 0.940 g/cm³. Thealpha-olefin utilized is usually 1-butene, 1-hexene, or 1-octene andZiegler-type catalysts are usually employed (although Phillips catalystsare also used to produce LLDPE having densities at the higher end of therange, and metallocene and other types of catalysts are also employed toproduce other well known variations of LLDPEs).

Ethylene α-olefin copolymers are copolymers having an ethylene as amajor component copolymerized with one or more alpha olefins such asoctene-1, hexene-1, or butene-1 as a minor component. EAOs includepolymers known as LLDPE, VLDPE, ULDPE, and plastomers and may be madeusing a variety of processes and catalysts including metallocene,single-site and constrained geometry catalysts as well as Ziegler-Nattaand Phillips catalysts.

Very Low Density Polyethylene (VLDPE) which is also called “Ultra LowDensity Polyethylene” (ULDPE) comprise copolymers of ethylene withalpha-olefins, usually 1-butene, 1-hexene or 1-octene and are recognizedby those skilled in the art as having a high degree of linearity ofstructure with short branching rather than the long side branchescharacteristic of LDPE. However, VLDPEs have lower densities thanLLDPEs. The densities of VLDPEs are recognized by those skilled in theart to range between 0.860 and 0.915 g/cm³. A process for making VLDPEsis described in European Patent Document publication number 120,503whose text and drawing are hereby incorporated by reference into thepresent document. Sometimes VLDPEs having a density less than 0.900g/cm³ are referred to as “plastomers”.

Polyethylenes may be used alone, in blends and/or with copolymers inboth monolayer and multilayer films for packaging applications for suchfood products as poultry, fresh red meat and processed meat.

As used herein, the term “modified” refers to a chemical derivative e.g.one having any form of anhydride functionality, such as anhydride ofmaleic acid, crotonic acid, citraconic acid, itaconic acid, fumaricacid, etc., whether grafted onto a polymer, copolymerized with apolymer, or otherwise functionally associated with one or more polymers,and is also inclusive of derivatives of such functionalities, such asacids, esters, and metal salts derived therefrom. Another example of acommon modification is acrylate modified polyolefins.

As used herein, terms identifying polymers, such as e.g. “polyamide” or“polypropylene,” are inclusive of not only polymers comprising repeatingunits derived from monomers known to polymerize to form a polymer of thenamed type, but are also inclusive of comonomers, as well as bothunmodified and modified polymers made by e.g. derivitization of apolymer after its polymerization to add functional groups or moietiesalong the polymeric chain. Furthermore, terms identifying polymers arealso inclusive of “blends” of such polymers. Thus, the terms “polyamidepolymer” and “nylon polymer” may refer to a polyamide-containinghomopolymer, a polyamide-containing copolymer or mixtures thereof.

The term “polyamide” means a high molecular weight polymer having amidelinkages (—CONH—)_(n) which occur along the molecular chain, andincludes “nylon” resins which are well known polymers having a multitudeof uses including utility as packaging films, bags, and casings. See,e.g. Modern Plastics Encyclopedia, 88 Vol. 64, No. 10A, pp 34-37 and554-555 (McGraw-Hill, Inc., 1987) which is hereby incorporated byreference. Polyamides are preferably selected from nylon compoundsapproved for use in producing articles intended for use in processing,handling, and packaging food.

The term “nylon” as used herein it refers more specifically to syntheticpolyamides, either aliphatic or aromatic, either in crystalline,semi-crystalline, or amorphous form characterized by the presence of theamide group —CONH. It is intended to refer to both polyamides andco-polyamides.

Thus the terms “polyamide” or “nylon” encompass both polymers comprisingrepeating units derived from monomers, such as caprolactam, whichpolymerize to form a polyamide, as well as copolymers derived from thecopolymerization of caprolactam with a comonomer which when polymerizedalone does not result in the formation of a polyamide. Preferably,polymers are selected from compositions approved as safe for producingarticles intended for use in processing, handling and packaging of food,such as nylon resins approved by the U.S. Food and Drug Administrationprovided at 21 CFR §177.1500 (“Nylon resins”), which is incorporatedherein by reference. Examples of these nylon polymeric resins for use infood packaging and processing include: nylon 66, nylon 610, nylon66/610, nylon 6/66, nylon 11, nylon 6, nylon 66T, nylon 612, nylon 12,nylon 6/12, nylon 6/69, nylon 46, nylon 6-3-T, nylon MXD-6, nylon MXDI,nylon 12T and nylon 6I/6T disclosed at 21 CFR §177.1500. Examples ofsuch polyamides include nylon homopolymers and copolymers such as thoseselected form the group consisting of nylon 4,6 (poly(tetramethyleneadipamide)), nylon 6 (polycaprolactam), nylon 6,6 (poly(hexamethyleneadipamide)), nylon 6,9 (poly(hexamethylene nonanediamide)), nylon 6,10(poly(hexamethylene sebacamide)), nylon 6,12 (poly(hexamethylenedodecanediamide)), nylon 6/12 (poly(caprolactam-co-dodecanediamide)),nylon 6,6/6 (poly(hexamethylene adipamide-co-caprolactam)), nylon 66/610(e.g., manufactured by the condensation of mixtures of nylon 66 saltsand nylon 610 salts), nylon 6/69 resins (e.g., manufactured by thecondensation of epsilon-caprolactam, hexamethylenediamine and azelaicacid), nylon 11 (polyundecanolactam), nylon 12 (polylauryllactam) andcopolymers or mixtures thereof.

In use of the term “amorphous nylon copolymer,” the term “amorphous” asused herein denotes an absence of a regular three-dimensionalarrangement of molecules or subunits of molecules extending overdistances which are large relative to atomic dimensions. However,regularity of structure may exist on a local scale. See, “AmorphousPolymers,” Encyclopedia of Polymer Science and Engineering, 2nd Ed., pp.789-842 (J. Wiley & Sons, Inc. 1985). In particular, the term “amorphousnylon copolymer” refers to a material recognized by one skilled in theart of differential scanning calorimetry (DSC) as having no measurablemelting point (less than 0.5 cal/g) or no heat of fusion as measured byDSC using ASTM 3417-83. The amorphous nylon copolymer may bemanufactured by the condensation of hexamethylenediamine, terephthalicacid, and isophthalic acid according to known processes. Amorphousnylons also include those amorphous nylons prepared from condensationpolymerization reactions of diamines with dicarboxylic acids. Forexample, an aliphatic diamine is combined with an aromatic dicarboxylicacid, or an aromatic diamine is combined with an aliphatic dicarboxylicacid to give suitable amorphous nylons.

As used herein, “EVOH” refers to ethylene vinyl alcohol copolymer. EVOHis otherwise known as saponified or hydrolyzed ethylene vinyl acetatecopolymer, and refers to a vinyl alcohol copolymer having an ethylenecomonomer. EVOH is prepared by the hydrolysis (or saponification) of anethylene-vinyl acetate copolymer. The degree of hydrolysis is preferablyfrom about 50 to 100 mole percent, more preferably, from about 85 to 100mole percent, and most preferably at least 97%. It is well known that tobe a highly effective oxygen barrier, the hydrolysis-saponification mustbe nearly complete, i.e. to the extent of at least 97%. EVOH iscommercially available in resin form with various percentages ofethylene and there is a direct relationship between ethylene content andmelting point. For example, EVOH having a melting point of about 175° C.or lower is characteristic of EVOH materials having an ethylene contentof about 38 mole % or higher. EVOH having an ethylene content of 38 mole% has a melting point of about 175° C. With increasing ethylene contentthe melting point is lowered. Also, EVOH polymers having increasing molepercentages of ethylene have greater gas permeabilities. A melting pointof about 158° C. corresponds to an ethylene content of 48 mole %. EVOHcopolymers having lower or higher ethylene contents may also beemployed. It is expected that processability and orientation would befacilitated at higher contents; however, gas permeabilities,particularly with respect to oxygen, may become undesirably high forcertain packaging applications which are sensitive to microbial growthin the presence of oxygen. Conversely lower contents may have lower gaspermeabilities, but processability and orientation may be moredifficult.

As used herein, the term “polyester” refers to synthetic homopolymersand copolymers having ester linkages between monomer units which may beformed by condensation polymerization methods. Polymers of this type arepreferable aromatic polyesters and more preferable, homopolymers andcopolymers of poly (ethylene terephthalate), poly (ethyleneisophthalate), poly (butylene terephthalate), poly (ethylenenaphthalate) and blends thereof. Suitable aromatic polyesters may havean intrinsic viscosity between 0.60 to 1.0, preferably between 0.60 to0.80.

“Reduced oxygen atmosphere” when referring to a packaged meat productrefers to a reduction in the partial pressure of oxygen in contact withthe packaged meat product, in comparison with the partial pressure ofoxygen in the Earth's atmosphere at standard temperature and pressure atsea level. Reduced oxygen atmosphere packages may include modifiedatmosphere packages where the oxygen partial pressure is less than thatof the Earth's atmosphere at standard temperature and pressure at sealevel, or vacuum packages, containing minimal gas pressure in contactwith the packaged meat.

“Meat” or “meat product” refers to any myoglobin or hemoglobincontaining tissue from livestock such as beef, pork, veal, lamb, mutton,chicken or turkey; game such as venison, quail, and duck; and fish,fishery or seafood products. The meat can be in a variety of formsincluding primals, subprimals, and retail cuts as well as ground,comminuted or mixed. The meat or meat product is preferably fresh, raw,uncooked meat, but may also be frozen, or thawed. It is further believedthat meat may be subjected to other irradiative, biological, chemical orphysical treatments. The suitability of any particular such treatmentmay be determined without undue experimentation in view of the presentdisclosure. As long as the myoglobin blooming agent containing film iseffective to promote, develop, enhance or maintain a desirable color itmay be advantageously employed to such end. Preferably the meat is lessthan 20 days post mortem. More preferably the meat is less than 12 daysor even 6 days or less post mortem.

Primal cuts of meat are also termed wholesale cuts and both terms referto large sections of a carcass that are usually sold and/or shipped tobutchers who further subdivide the primal into subprimals and individualretail cuts for sale to consumers. Examples of primal cuts of beef are:round; rump; loin end; flank; short loin; plate; rib; brisket; shank;and chuck. Examples of pork primals include: loin; leg; shoulder; andbelly.

Subprimals are intermediate in size and may be divided further intoretail cuts or are sometimes sold as retail cuts. Beef subprimalsinclude: arm; blade; ribs; beef plate; top round; bottom round; ribs;top butt; bottom butt; tenderloin; and top loin. Pork subprimalsinclude: butt shoulder; picnic shoulder; center cut; sirloin; butt end;shank end; side pork and side rib.

Retail cuts of meat are consumer cuts made by dividing wholesale cutsinto smaller pieces. Examples of retail cuts of beef include: steakssuch as round, top round, cubed, sirloin, t-bone, porterhouse, filetmignon, rib eye, rib, skirt, flank, and tip; roasts such as blade, pot,and chuck; corned brisket; fresh brisket; stew beef; short ribs; kabobs;eye of round; rolled rump; shank cross cuts; steak rolls; ground beef;and beef patties. Examples of retail cuts of pork include: arm roastsand steaks; spareribs; bacon; salt pork; ham; ham steaks; ham slices;pork tenderloin; chops; cutlets; fat back; sausage; links; and groundpork.

“Fresh meat” means meat that is uncooked, uncured, unsmoked andunmarinated. “Fresh meat” includes post mortem meat that has beenphysically divided, for example, by cutting, grinding or mixing. Thereis no added salt in fresh meat that has not been enhanced. Naturallyoccurring sodium typically is less than 50 mg/100 g of meat and accountsfor a salt content of less than about 0.15, preferably less than 0.128wt. %. Values of sodium are in a data base for nutritional compositionof meat called the “National Nutrient Data Bank”, and the data ispublished in Agriculture Handbook No. 8, “Composition of Foods—Raw,Processed, Prepared” referred to in the industry as “Handbook 8” both ofwhich are hereby incorporated by reference.

“Enhanced meat” means meat that has added water mixed with otheringredients such as sodium chloride, phosphates, antioxidants, andflavoring e.g. to make meat moist, more tender and to help enhanceshelf-life. Fresh beef, pork or poultry after being “enhanced” wouldtypically contain 0.3-0.6 wt. % salt (sodium chloride).

“Processed meat” means meat that has been changed by heat and chemicalprocesses, e.g., by cooking or curing. Cooked ham, hot dogs, and lunchmeat are examples of cured processed meat.

“Uncured processed meats” are processed meats that do not containnitrites or nitrates. Uncured processed meats would typically containgreater than 1.0% by weight, typically 1.2-2.0 wt. %, sodium chloride(salt). Cooked roast beef and bratwurst are examples of uncuredprocessed meat.

“Cured meat” means meat that is preserved through direct addition ofnitrite (or nitrate which is converted to nitrite) e.g. having at least50 ppm sodium nitrite and at least 1% by wt. added salt, i.e. sodiumchloride, for the purpose of preservation by retarding bacterial growth.Nitrites, nitrates or blends thereof are commonly present with sodiumchloride in curing compositions. “Uncured meat” does not contain addednitrite or nitrate. Wet cured meats are soaked in salt brine. Dry curedmeats have salt applied to the surface. Injection cured meats have thecuring salts (cure) applied by needle injection into the meat.

Cured processed meats often have 2-3.5 wt. % salt. A brine content of3.5-4.0 wt. % (2.6-3.0% on a weight basis in treated meat) as the levelof sodium chloride salt (potassium chloride may be substituted for someor all of the NaCl) is needed in processed meat to adequately slow downbacterial growth to permit 60-90 day shelf life, although other means ofpreservation may also be employed to maintain shelf life at reduced saltlevels. According to Pegg, R. B. and F. Shahidi, 2000. Nitrite Curing ofMeat. Food & Nutrition Press, Inc. Trumbull, Conn. 06611 cured meats mayhave typical salt levels of 1.2-1.8 wt. % in bacon, 2-3 wt. % in hams,1-2 wt. % in sausages and 2-4 wt. % in jerkies. It is believed thatfresh meat such as beef, pork and poultry has no nitrite or nitratenaturally occurring or added. The United States Department ofAgriculture (USDA) permits ingoing nitrite and nitrate for cured andprocessed meat at a level up to a maximum of 625 ppm sodium nitrite or2,187 ppm sodium nitrate in dry cured products. In other applicationslevels have different limits e.g. in typical cooked whole muscle meatproducts the limit as sodium nitrite is 156 ppm and in comminuted meats,200 ppm. The maximum nitrite usage level in hot dogs or bologna istypically 156 ppm, while that for bacon is 120 ppm. Sodium ascorbate (orsimilar compounds) may be present in these cures.

In Europe it is believed that the minimum level of salt and nitriterequired by law for curing is 1.0 wt. % and 50 ppm respectively. TheUSDA has stated: “As a matter of policy, the Agency requires a minimumof 120 ppm of ingoing nitrite in all cured “Keep Refrigerated” products,unless the establishment can demonstrate that safety is assured by someother preservation process such as thermal processing, pH or moisturecontrol. This 120 ppm policy for ingoing nitrite is based on safety datareviewed when the bacon standard was developed.” (See, “ProcessingInspectors' Calculations Handbook”, Chapter 3, p. 12, revised 1995). TheHandbook also states: “There is no regulatory minimum ingoing nitritelevel however 40 ppm nitrite is useful in that it has some preservativeeffect. This amount has also been show to be sufficient for color-fixingpurposes and to achieve the expected cured meat or poultry appearance.”

The meat product can be any meat suitable for human consumption thatcontains a myoglobin like molecule. References to total myoglobin in ameat product refer to the amount of the myoglobin like molecules thatare physiologically present in the meat tissue prior to harvesting forhuman consumption. Specific meat products contain a level of myoglobinsufficient to provide its characteristic color. Examples of suitablefresh meat cuts include beef, veal, pork, poultry, mutton, and lamb. Theconcentration of myoglobin varies in these different types of meatproducts. For example, beef typically contains about 3-20 mg ofmyoglobin per gram of meat, pork contains about 1-5 mg myoglobin pergram of meat, chicken contains less than about 1 mg myoglobin per gramof meat. Thus, the concentration of total myoglobin compounds in theabove described meat products is typically between about 0.5 mg and 25mg of myoglobin compounds per gram of the meat product.

In fresh meat (postmortem muscle tissue), oxygen can continuallyassociate and disassociate from the heme complex of the myoglobinmolecule. It is the relative abundance of three forms of the musclepigment that determines the visual color of fresh meat. They includepurple deoxymyoglobin (reduced myoglobin), red oxymyoglobin (oxygenatedmyoglobin); and brown metmyoglobin (oxidized myoglobin). Thedeoxymyoglobin form typically predominates immediately after the animalis slaughtered. Thus, freshly cut meat can have a purple color. Thispurple color can persist for a long time if the pigment is not exposedto oxygen. Cutting or grinding exposes the pigment to oxygen in theatmosphere, and the purple color can quickly convert to either brightred (oxymyoglobin) or brown (metmyoglobin). Thus, althoughdeoxymyoglobin is technically indicative of fresher meat, it is the redor “bloomed” meat color that consumers use as their primary criterionfor perceiving freshness. It is believed without wishing to be bound bythe belief that the preferred red color of fresh meat occurs when atleast 50% of the deoxymyoglobin molecules are oxygenated to theoxymyoglobin state. Changes in the relative percentage of each of theseforms can continue to occur as fresh meat is exposed to oxygen forlonger periods of time. The immediate conversion of the purple color tothe desirable bright red or undesirable brown can depend on the partialpressure of oxygen at the surface. The purple color is favored at thevery low oxygen level, and can dominate at oxygen levels of 0-0.2% byvolume. The brown color is favored when the partial pressure of oxygenis only slightly higher (0.2% to 5.0%). Consumer discriminationtypically begins when the relative amount of metmyoglobin is 20%. Adistinctly brown color is evident at 40% metmyoglobin, which typicallyrenders the meat unsaleable even though it remains nutritious andhealthy for consumption.

Certain biochemical reactions that occur in muscle tissue after deathcan also affect fresh meat color, such as the presence of activeglycolytic enzymes that convert oxygen to carbon dioxide. Reducingcoenzymes called metmyoglobin reductases present in meat convertmetmyoglobin back to deoxymyoglobin, and their activity is called “MRA”which is an abbreviation for metmyoglobin reducing activity. MRA can bedescribed as the ability of muscle to reduce metmyoglobin back to itsnatural deoxymyoglobin state. MRA is lost when the oxidizable substratesare depleted or when heat or acid denatures the enzymes. When theenzymes lose their activity or are denatured, the iron of the hemepigment automatically oxidizes to the metmyoglobin form, and the browncolor stabilizes and dominates. MRA persists for a period of time afterdeath depending on the amount of exposure of the meat tissue to oxygen.During this time oxygen is continually consumed by the meat tissue. Theoxygen consumption rate is referred to as “OCR”. When meat that has ahigh OCR is exposed to oxygen, the oxygen tension is reduced so rapidlythat the metmyoglobin is favored below the viewing surface. If it isclose to the viewing surface, the perceived color of the meat isaffected. The MRA is important to minimize this layer of metmyoglobinthat forms between the bloomed surface and purple interior. As the MRAwears out, the brown metmyoglobin layer thickens and migrates toward thesurface, thus terminating display life. When the MRA is high, themetmyoglobin layer is thin and sometimes not visible to the naked eye.

MRA and OCR relate to determining the types of packaging best suited forretail sale in order to prolong the desirable appearance of meat as longas possible. Hermetically sealed packages with films that are a barrierto oxygen will cause a low oxygen tension on the meat surface. Thus,metmyoglobin formation occurs and the viewing surface changes to anundesirable brown color. However, if the OCR is high enough to keepahead of the oxygen that migrates across the packaging film, and the MRAis good enough to reduce metmyoglobin that forms on the surface, thennative deoxymyoglobin replaces metmyoglobin. After a period of time, theperceived color changes from brown to purple. Both of these colors areunacceptable to the consumer. For this reason, vacuum packaging byitself has historically been an unacceptable format for case ready freshmeat although it is used to ship subprimal and other large cuts of meatfrom the slaughterhouse to retail butchers for further processing andre-packaging. On the other hand, vacuum packaging is the format ofchoice for cooked and cured processed meats where the myoglobin pigmentis denatured by heat. Heat from cooking causes the globin portion of thenitrosylated myoglobin molecule to denature and separate from the hemeportion. It is the nitrosylated heme complex that gives cured andprocessed meats their characteristic color. When oxygen is eliminatedfrom a cured processed meat package, the product's color and flavor candeteriorate slower than when oxygen is present. In the present inventionoxygen must be removed from the environment of the meat before thepreferred color can develop. A certain amount of oxygen penetrates themeat after slaughter and fabrication. This oxygen is eliminated by theOCR/MRA activities. Similarly those activities facilitate the dominanceof the deoxymyoglobin form of the myoglobin molecule. It is believed butnot wishing to be bound by the belief that the OCR/MRA activities alsofacilitate the reduction of nitrite to nitric oxide. The formation ofdeoxymyoglobin and nitric oxide allows for the bloomed colordevelopment. Oxygen itself is a blooming agent because it causes theformation of oxymyoglobin as described earlier herein. However, oxygeninterferes with the reactions that form deoxymyoglobin and nitric oxide.Therefore, it interferes with the bloomed color development in thepresence of nitrite. Thus, it is a preferred aspect of the presentinvention that an oxygen barrier layer is selected and configured toprotect the meat surface from the ingress of atmospheric oxygen duringthe formation of the desired bloomed meat color.

Myoglobin Blooming Agents

A “myoglobin blooming agent” refers to any agent (or precursor thereof)that binds to or interacts with any myoglobin-containing structure(including but not limited to deoxymyoglobin, oxymyoglobin,metmyoglobin, carboxymyoglobin, and nitric oxide myoglobin) present in afresh meat product to produce or preserve a desired color, such as a redcolor indicative of fresh meat. The myoglobin blooming agent may alsointeract or cause an interaction with hemoglobin present in a meatproduct so as to produce, maintain or enhance i.e. “fix” a desiredcolor. Thus, the myoglobin blooming agent is not a color additive, butit acts as a color fixative. In one preferred embodiment, the myoglobinblooming agent is a “nitric oxide donating compound” (“NO donor”) thatprovides a nitric oxide (NO) molecule that binds to the myoglobinpresent in a meat product so as to maintain or promote a reddening orblooming or other favorable coloration of the meat product. A nitricoxide donating compound releases nitric oxide or is a precursor e.g.nitrate which acts as an intermediate leading to the formation of nitricoxide which binds to a myoglobin molecule in a meat product. In a firstaspect, the myoglobin blooming agent is a nitrate (MNO₃) or nitrite(MNO₂) salt, where suitable metal counter ion (M⁺) can be selected fromthe group consisting of: alkali metals (e.g. sodium, potassium),alkaline earth metals (e.g. calcium), transition metal, ammonium and orprotonated primary, secondary, or tertiary amines or quaternary amines.In a second aspect, the myoglobin blooming agent comprises a Fremy'ssalt [NO(SO₃Na)₂ and NO(SO₃K)₂]. Other suitable nitric oxide donatingagents are disclosed in U.S. Pat. No. 6,706,274 to Herrmann et al.(filed Jan. 18, 2001), U.S. Pat. No. 5,994,444 to Trescony et al. (filedOct. 16, 1997), and U.S. Pat. No. 6,939,569 to Green et al. (filed Jun.18, 1999), as well as published U.S. Patent Application No.US2005/0106380 by Gray et al. (filed Nov. 13, 2003). The myoglobinblooming agent may be a salt, particularly a nitrite or nitrate salt.Sodium nitrate or sodium nitrite or blends thereof may typically beused. Potassium nitrate or potassium nitrite may also be used.Additionally suitable compounds may include a nitrogen containing agentthat promotes the release or formation of NO such as nitrite reductase,nitrate reductase or nitrosothiol reductase catalytic agents, includingthe materials described in WIPO Publication No. WO 02/056904 byMeyerhoff et al. (filed Jan. 16, 2002), which is incorporated herein byreference. It is expected that these agents and compounds would besuitable myoglobin blooming agents. Other suitable agents may includesulfur containing compounds that similarly bind or act as precursors orintermediates to agents that fix a desirable color by binding tomyoglobin.

Myoglobin blooming agents and solutions or dispersions thereof may becolorless such as sodium nitrate, or e.g. such as sodium nitrite mayhave an intrinsic pale color (i.e. may not be totally colorless), butthis color does not typically have sufficient intensity itself to act asa significant colorant or color additive. However, this does notpreclude either the use of colored myoglobin blooming agents whichimpart an intrinsic color or the combination of a myoglobin bloomingagent in combination with one or more natural and/or artificialcolorants, pigments, dyes and/or flavorants such as annatto, bixin,norbixin, beet powder, caramel, carmine, cochineal, turmeric, paprika,liquid smoke, one or more FD&C colorants, etc.

The myoglobin blooming agent is believed to cause an interaction withmyoglobin in meat products, thereby maintaining, promoting or enhancinga desirable meat color. Myoglobin includes a non-protein portion calledheme and a protein portion called globin. The heme portion includes aniron atom in a planar ring. The globin portion can provide athree-dimensional structure that surrounds the heme group and stabilizesthe molecule. The heme group provides an open binding site that can bindcertain ligands having the proper shape and electron configuration tobond to the iron atom. When a ligand enters and binds to the hemepocket, the electron configuration of the ligand can change the shape ofthe globin portion of the molecule in a manner that affects lightabsorption characteristics of the heme group. Therefore, the presence orabsence of a ligand such as oxygen in the heme pocket, and the liganditself can result in visible color changes of myoglobin.

When there is no ligand in the heme pocket, myoglobin is calleddeoxymyoglobin, which has a purple color (which is sometimescharacterized as a deep red, dark red, reddish blue or bluish red).Molecular oxygen, O₂ (“oxygen”) readily acts as a ligand that binds tothe heme group, permitting biological transport of oxygen from the bloodstream to the mitochondria within cells. When oxygen binds to the hemepocket, purple deoxymyoglobin becomes oxymyoglobin, characterized by ared color. Upon dissociation of the oxygen ligand from oxymyoglobin, theiron atom is oxidized leaving the iron in the ferric state. As thechemical state of iron can change from ferrous (Fe²⁺) to ferric (Fe³⁺),the three-dimensional structure of the globin part can change in amanner that allows water molecules to bind to the heme pocket. Bindingof a water molecule in the ferric iron containing heme pocket affectslight absorption of the heme pocket. The oxidized form of myoglobin witha water molecule in the heme group is referred to as metmyoglobin andits color is brown. The oxidation of the iron atom is believed to resultin a brown color. Heme ligands other than oxygen or water may alsoaffect meat color. For example, the presence of cyanide or fluorine cancause an undesirable brown meat color, and the presence of carbonmonoxide (CO) may cause a desirable bright red color similar to oxygen.Although it has been suggested that nitric oxide (NO) can cause a dullred (or stable pink in the case of cured meat which also contains sodiumchloride, it has been discovered that in the absence of oxygen NO mayproduce a desired bright red color similar to that caused by oxygen inuncooked meat, especially in fresh, raw, unprocessed or uncured meat. Ithas been discovered that the development of this desired bright redcolor may take many hours and typically may take from 1 to 5 days andthat initially the meat color in a vacuum package having an oxygenbarrier may turn to an undesirable brown until the unexpectedtransformation to the desired red takes place.

Other variables that affect the stability of the globin portion alsoaffect the affinity of the heme group for oxygen and the tendency of thechemical state of the iron atom to become oxidized. Acidity and hightemperature, such as that associated with cooking, can denature theglobin part thus leading to instability of the heme group. In theabsence of stabilizing ligands the oxidation of the heme iron isautomatic when the globin is denatured.

Heat-Shrinkable Food Packaging Films

In the present invention, heat shrinkable, oxygen barrier, foodpackaging films having a food contact surface comprising a myoglobinblooming agent are provided. A “food contact surface” refers to theportion of a packaging material that is designed to contact a packagedmeat product surface. Preferably, the food packaging film includes afood contact surface comprising a myoglobin blooming agent in an amounteffective to promote or maintain a desirable color after contact with ameat product. The myoglobin blooming agent (MBA) preferably will contactthe meat surface in an amount sufficient to produce a desired red colorwhich preferably does not penetrate to an undesirable depth of the foodthickness under reduced oxygen conditions (this color may take awhile todevelop e.g. 1 to 5 days). Beneficially the MBA may be present on thefilm food contact surface (or on the myoglobin food surface) in anamount of from about 0.05 to 3 to 5 to 10 μmoles/in² and in incrementsof 0.1 μmole thereof. Greater or lesser amounts of MBA may be used andthe color intensity may thereby be varied depending upon the relativepresence or absence of myoglobin.

Thus, the food contact surface of the heat shrinkable film preferablycontains a myoglobin blooming agent in a concentration high enough toproduce and/or maintain a desired surface coloration of a fresh meatproduct, but low enough to prevent undesirable extension of the colorinto the body of the meat product. Preferably, the myoglobin bloomingagent is present on a food contact surface in a concentration that issufficient upon contact with a meat surface to convert at least 50% ofthe targeted myoglobin molecules to a desired ligand binding state. Theavailable amount or concentration of myoglobin blooming agent ispreferably selected to bind ligands producing desirable coloration ofthe meat to the myoglobin molecules in the outermost ¼-inch, or ⅙, ⅛,1/10, 1/12, 1/16 or 1/20-inch or less of the meat product, althoughdeeper penetrations may be accomplished if desired. For example, anitric oxide donating myoglobin blooming agent is desirably present in aconcentration sufficient to convert at least 50% of the myoglobinmolecules on the contacting meat surface to nitric oxide myoglobin. Themyoglobin blooming agent may be coated on a monolayer film or on theinterior layer of a multilayer film or it may be incorporated therein.

The myoglobin blooming agent is preferably evenly or uniformlydistributed on the surface of the food contact surface The minimumamount required to cause the desired coloration depends on theconcentration of myoglobin present in the food product. For example,beef products containing 10 mg/gm of myoglobin may require 10 times moremyoglobin blooming agent than poultry products containing 1 mg/gm ofmyoglobin. Also, if the desired depth of penetration is 0.25 inches,then in order to affect all of the myoglobin molecules (molecular weightof myoglobin is about 17,000 g/mole) in 1 square inch of beef to a depthof 0.25 inches, there would have to be at least 2.4 umoles of themyoglobin blooming agent available for transfer via the surface of 1square inch of film (one square inch of beef to a depth of about 0.25inches equals about 4.1 grams of meat (specific gravity of 1 gm/cc)).Sodium nitrite as a preferred myoglobin blooming agent has a molecularweight of 69 g/mole. Thus 2.4 umoles of NaNO₂ weighs 0.166 mg and thetotal amount of myoglobin in 4.1 grams of meat containing 10 mg/gm is 41mg. Beef meat typically contains myoglobin at a level of 3-10 mg/gm. Thepreferred amount of myoglobin blooming agent that would be present onthe film beef is 0.72-2.4 umoles/in². Similarly pork contains myoglobinat a level of 1-3 mg/gm. A packaging film for this application wouldprovide 0.24-0.72 umoles/in². Poultry having less than 1 mg/gm ofmyoglobin would preferably use a film providing less than 0.24umoles/in² e.g. 0.12 umoles/in². A film using sodium nitrite (MW=69g/mole) as a myoglobin blooming agent would preferably provide0.050-0.166 mg/in² for beef meat products; 0.017-0.050 mg/in² for porkmeat products; and less than 0.017 mg/in² for poultry meat products. Afilm providing 0.17 mg/in² would be suitable for a variety of types offresh meat.

A higher amount of sodium nitrite may be preferred for darker coloredmuscles that may contain higher levels of myoglobin. When the myoglobinblooming agent is incorporated into the polymer matrix that comprisesthe food contact layer of a monolayer or multilayer packaging film onlya portion of it is able to effectively migrate from the film surfaceinto the products surface. Film inclusion levels of up to 20 times orhigher of the amount required for effective color fixing is anticipated.

Thus, the amount of myoglobin blooming agent per unit area of the foodcontact surface can be selected to provide a desired food coloration ofa packaged fresh meat product surface. For example, the food contactlayer can include about 0.005 to about 0.900 mg/in² of a myoglobinblooming agent such as sodium nitrite, preferably about 0.010 to about0.400 mg/in² and most preferably about 0.100 to about 0.300 mg/in². Forbeef products, a food contact layer may include e.g. about 0.200 toabout 0.250 mg/in² e.g. of a sodium nitrite myoglobin blooming agent,while lower concentrations e.g. of about 0.100 to about 0.150 mg/in² maybe used for pork products.

A uniform dispersion or coating having particle size of 35 micrometers(μ) or less, preferably 10μ or less (fineness of grind of 4 gu or less)is desirable. Although larger particle sizes may also be used, the filmprior to use is less aesthetically pleasing. If particle size is toolarge, an initial spotty appearance may result although results tend toeven out and become more uniform over time and such desirable coloruniformity (i.e. lack of spottiness or blotches) is often present uponcolor transformation from brown to red. Advantageously, the myoglobinblooming agent may be applied in a manner to wet out the surface of thefood contact surface layer of the film using film forming agents,surfactants, binding agents and other compounds for the purpose. Forexample, the myoglobin blooming agent according to the present inventionmay be sprayed on a food contact surface of the film. Tubular films andcasings also may be coated by other means (including the well knownmethods of dipping and slugging). Typical myoglobin blooming agents donot easily pass through the film wall and therefore it is preferable toslug the myoglobin blooming agent inside the tube and/or apply themyoglobin blooming agent to the inner surface of the tube during e.g. ashirring operation via a spray, because external application e.g. bydipping would require a complex and more costly operation of turning thetube inside out to provide contact between the myoglobin blooming agentand the meat contact surface. Application of other additives and coatingcompositions via solution spraying during or just prior to shirring isconvenient, economical and facilitates placement of a regular measureddistribution of a coating on the interior tube surface. For example,lubricants and other compositions have been applied by various meanssuch as slugging, spraying, or contact coating the inner surface of atubular polymeric casing via a shirring mandrel and such means are wellknown (See e.g. U.S. Pat. No. 3,378,379 (Shiner); U.S. Pat. No.3,451,827 (Bridgeford); U.S. Pat. No. 4,397,891 (Kaelberer et al); U.S.Pat. No. 5,256,458 (Oxley et al); U.S. Pat. No. 5,573,800 (Wilhoit); andU.S. Pat. No. 6,143,344 (Jon et al) which are all incorporated byreference in their entireties.) Plastic casings made according to thepresent invention, may be coated with the inventive myoglobin bloomingagent preferably by slugging to provide a uniformly thick coating.

Tubular forms or nontubular (e.g. sheets or webs) forms of the heatshrinkable film may be coated by dry or wet spraying or dusting or byroll coating or coating using a Meyer bar or doctor blade, or byprinting means e.g. using gravure or flexography printing or by usingelectrostatic transfer. Also, application may occur at various points inthe manufacturing process including for example, by blending,incorporation in a masterbatch or addition to the polymeric layer priorto extrusion, or by dusting, spraying or coating during or afterextrusion or during bubble or tube formation or during winding, or bagmaking e.g. in a dusting or powdering step.

In one embodiment of the invention, it is contemplated that a foodcontact surface layer may comprise between about 1,000 ppm (0.1%) andabout 50,000 ppm (5.0%) of a myoglobin blooming agent such as sodiumnitrite, more preferably about 5,000 ppm to about 25,000 ppm, and mostpreferably about 7,500 ppm to about 20,000 ppm. Typically, a foodcontact surface layer comprises about 1.5 wt. % to about 2.0 wt. % orless (15,000 ppm-20,000 ppm) of a nitrite salt for packaging a freshground beef product, or about 0.75 wt. % to about 1.5 wt. % of a nitritesalt for packaging a fresh pork meat product. Amounts in a range of 0.75to 2.25 wt. % may be advantageously employed for a variety of meats.

According to the invention, single-layer heat-shrinkable packaging filmsmay be provided that comprise a myoglobin blooming agent. In anotherembodiment the heat-shrinkable film may also be a multilayer film. Theinventive heat shrinkable packaging films can have any suitablecomposition or configuration. Preferably, the heat-shrinkable packagingfilm fulfills multiple functional requirements which may be present inone or more or a combination of layers. For example a single layer filmmay combine the functions of oxygen barrier, heat shrinkability, andmyoglobin blooming agent contact with one or more additional functionssuch as puncture resistance, abuse resistance, printability, moisturebarrier, heat sealability, transparency, high gloss, low toxicity, hightemperature resistance, low temperature flexibility, etc. Alternatively,multiple layers may be employed to add functionality. The presentinvention is adapted for use in a wide variety of commercially availablepackaging films such as those sold by: Curwood, Inc. under thetrademarks ABP, Clear-Tite, Cook-Tite, Perflex, Pro-Guard, Pro-Tite, andSurround; and by others e.g. marketed under the Alcan, Cryovac,Krehalon, Vector, and Viskase, brands. A typical beneficial heatshrinkable film according to the present invention may have an interiorsurface food contact layer which also serves as a sealant layer, and aheat resistant and abuse resistant exterior surface layer with a corelayer there between which comprises an oxygen barrier material. Anothercommon suitable film has adhesive layers on either side of the coreoxygen barrier layer to connect with the surface layers.

The multilayer heat-shrinkable film embodiments of the present inventionmay have an exterior surface and an interior surface, and include 2, 3,4, 5, 6, 7, 8, 9, or more polymeric thermoplastic film layers havingdesirable levels of free shrink.

Film Thickness

Preferably, the heat shrinkable film has a total thickness of less thanabout 10 mils, more preferably the film has a total thickness of fromabout 0.5 to 10 mils (12.5-250 microns (μ)). Advantageously manyembodiments may have a thickness from about 1 to 5 mils, with certaintypical embodiments being from about 1.5 to 3 mils. For example, entiresingle or multilayer films or any single layer of a multilayer film canhave any suitable thicknesses, including 1, 2, 3, 4, 5, 6, 7, 8, 9, or10 mils, or any increment of 0.1 or 0.01 mil therebetween. Thicker andthinner films are also provided. Although suitable films for packagingfoodstuffs as thick as 4 mils (101.6 microns) or higher, or as thin as 1mil (25.4 microns) or less may be made, it is expected that the mostcommon films will be between about 1.5-3 mil (38-76 microns). Especiallypreferred for use as films for food packaging are films where themultilayer film has a thickness of between about 2 to 3 mils (50.8-76.2microns). Such films may have good abuse resistance and machinability.

The inventive films are heat shrinkable and have at least 10% freeshrink in at least one direction at 90° C. or less as more fullydescribed below. Preferably certain embodiments of the invention mayhave at least 20% shrink at 90° C. in at least one direction (preferablyboth directions) and advantageously may have at least 30% shrink at 90°C. in at least one direction, and preferably may have at least 25% inboth MD and TD directions. Advantageously, the packaging films may havea total free shrink at 90° C. of at least about 30%, more preferably atleast 40% or 60% or more.

By being heat shrinkable the film containing a myoglobin blooming agentis brought into intimate contact with the surface of a myoglobincontaining food product thereby effecting the transfer of the agent tothe food to promote and/or maintain the desired red food color. Pointsof non-contact may cause meat or bone to remain an undesirable colorsuch as purple under vacuum packaging conditions. Beneficially, heatshrinkable film provides tight, attractive packaging for consumers.

Food Contact/Heat Sealing Layers

It is essential that the heat shrinkable oxygen barrier film of thepresent invention have a food contact layer. This food contact layer mayalso function as a heat sealing or heat sealable layer to facilitateformation of hermetically sealed packages, although tubular plasticcasings may also be used and sealed e.g. by clips as known in the art.Preferred films of the present invention utilize a food contact layerwhich has heat sealing properties.

The terms “heat sealing layer” or “sealant layer” are usedinterchangeably to refer to a layer which is heat sealable i.e., capableof fusion bonding by conventional indirect heating means which generatesufficient heat on at least one film contact surface for conduction tothe contiguous film contact surface and formation of a bond interfacetherebetween without loss of the film integrity. The bond interfacebetween contiguous inner layers preferably has sufficient physicalstrength to withstand the packaging process and subsequent handlingincluding e.g. tensions resulting from stretching or shrinking attendantwith the presence of a food body sealed within a package utilizing afilm having a heat sealable layer. Advantageously, the bond interface ispreferably sufficiently thermally stable to prevent gas or liquidleakage therethrough when exposed to above or below ambient temperaturese.g. during one or more of the following: packaging operations, storage,handling, transport, display, or processing of food. Heat seals may bedesigned to meet different conditions of expected use and various heatseal formulations are known in the art and may be employed with thepresent invention. In certain optional embodiments heat seals may besubjected to pasteurization or cook-in temperatures and conditions, e.g.in a sealed bag or sealed tray form. For use in cook-in applicationsheat seals should withstand elevated temperatures up to about 160-180°F. (71-82° C.) or higher e.g. 212° F. (100° C.) for extended periods oftime e.g. up to 4 to 12 hours in environments which may range fromheated humidified air or steam to submersion in heated water. Preferablythe food contact or heat seal layer is heat sealable to itself, but maybe sealable to other objects, films or layers e.g. to a tray when usedas a lidding film, or to an outer layer in a lap seal or in certain trayoverwrap embodiments. Also in certain embodiments the myoglobin bloomingagent containing food contact layer need not be heat sealable.

A sealing layer is preferably positioned at or near the interior surfaceof the packaging film, and can be an interior surface layer which allowsa monolayer or multilayer film to be formed into a resulting package orbag. The sealant layer may comprise a myoglobin blooming agent and asuitable heat-sealable polymer such as an ethylene-α-olefin copolymer.The exterior layer may also be a heat sealable layer and used in placeof or in addition to the interior layer for this purpose.

The food contact layer may comprise a sealant layer and may comprise aheat sealable polymeric material such as a polyolefin or blend thereofe.g. polyethylenes such as LDPE, HDPE, ethylene α-olefin copolymersincluding e.g. plastomers, VLDPE, LLDPE or polypropylene homopolymers,polypropylene copolymers, or homogeneous polyolefin resins, such asthose made with constrained geometry catalysts or metallocenesingle-site catalysts, including e.g. copolymers of ethylene orpropylene with at least one C_(4-8 or higher) α-olefins (e.g. butene-1,hexene-1 or octene-1 or combinations thereof) with a majority ofpolymeric units derived from ethylene or propylene. Ethylene vinylacetate (EVA) copolymers, EBAs, EMAs, EMAAs or EEAs are also suitablematerials for forming the inner surface heat sealable layer. A foodcontact and/or sealant layer may also comprise an ionomer which isessentially a metal salt neutralized copolymer of ethylene and acrylicor methacrylic acid, Suitable sealant/food contact layer materials ofteninclude ionomers, polyolefins or blends thereof, such as those disclosedin U.S. Pat. Nos. 6,815,023; 6,773,820; 6,682,825; 6,316,067; and5,759,648; 5,663,002; and U.S. Patent Application Publication Nos.:2005/0129969 (Schell et al); and 2004/0166262 (Busche et al.). Foodcontact or sealant layers may also comprise nylon or polyesters such aspolyester terephthalate (PET) or copolymers or blends thereof. The foodcontact layer may be 100% of the thickness of, the total structure. Thefood contact or sealant layers in multilayer structures may be of anythickness with thicknesses in multilayer structures of up to 1% to 5% to15% to 50% or more of the total thickness contemplated. Preferredexamples of such sealable resins comprising a food contact and/orsealant layer include ethylene α-olefin copolymers commerciallyavailable from: Dow Chemical Company under a trade name of “AFFINITY” or“ELITE” (including octene-1 as α-olefin); and ExxonMobil Co. under atrade name of “EXACT” (including hexene-1 as comonomer); and ionomerscommercially available from DuPont Company under the trade name Surlyn®.

Barrier Layers

Barrier layers can be made comprising a myoglobin blooming agent. Thebarrier layer preferably function as a gas barrier layer, although othertypes of barriers such as moisture barrier layers can also include themyoglobin blooming agent. The gas barrier layer is preferably an oxygenbarrier layer, and is preferably a core layer positioned between thefirst and second layers. For example, the oxygen barrier layer can be incontact with a first surface layer and an adhesive layer or may besandwiched between two tie layers and/or two surface layers.

To achieve all the benefits of the present invention it is essentialthat the myoglobin blooming agent film be used in a package incombination with a reduced oxygen atmosphere. In one aspect, an oxygenbarrier is used in the meat package or packaging film that is maintainedat a reduced oxygen atmosphere. The oxygen barrier is preferablyselected to provide an oxygen permeability sufficiently diminished topermit a desirable color to be induced or maintained within the packagedmeat. For example, a film may comprise an oxygen barrier having anoxygen permeability that is low enough to reduce the activity ofmetmyoglobin reducing enzymes to reduce myoglobin in the meat, and/ormaintain a reduced oxygen atmosphere in contact with the meat to reduceoxygen binding to myoglobin on the surface of the packaged fresh meat.

The barrier layer can comprise any suitable material, such as nylon,EVOH or PVDC. The barrier layer can provide a suitable barrier to oxygenfor the desired preservation of the article to be packaged under theanticipated storage conditions. An oxygen barrier layer can compriseEVOH, polyvinylidene chloride, polyamide, polyester, polyalkylenecarbonate, polyacrylonitrile, nanocomposite, a metallized film such asaluminum vapor deposited on a polyolefin, etc., as known to those ofskill in the art. The barrier layer preferably also provides desirableoptical properties when stretch oriented, including transparency and lowhaze and a stretching behavior compatible with the layers around it. Itis desirable that the thickness of the barrier layer be selected toprovide the desired combination of the performance properties soughte.g. with respect to oxygen permeability, shrinkage values especially atlow temperatures, ease of orientation, delamination resistance, andoptical properties. Suitable thicknesses in multilayer films are lessthan 15%, e.g. from 3 to 13% of the total film thickness and preferablyless than about 10% of the total thickness of the multilayer film.Greater thicknesses may be employed however oxygen barrier polymers tendto be relatively expensive and therefore it is expected that less costlyresins will be used in other layers to impart desirable properties oncea suitable thickness is used to achieve the desired gas barrier propertyfor the film layer combination. For example, the thickness of a coreoxygen barrier layer may advantageously be less than about 0.45 mil(10.16 microns) and greater than about 0.05 mil (1.27 microns),including 0.10, 0.20, 0.25, 0.30, 0.40, or 0.45 mil thick.

Preferably, multilayer films include a core oxygen barrier layer. Anysuitable material can be used to form an oxygen barrier layer. Theoxygen barrier layer of a film may comprise EVOH, although oxygenbarrier layers comprising polyvinylidene chloride-vinyl chloridecopolymer (PVDC or VDC-VC) or vinylidene chloride-methylacrylatecopolymer (VDC-MA) as well as blends thereof, can also be used. Onepreferred EVOH barrier material is a 44 mol % EVOH resin E151B sold byEval Company of America, under the trade name Eval® LC-E151B. Anotherexample of an EVOH that may be acceptable can be purchased from NipponGohsei under the trade name Soamol® AT (44 mol % ethylene EVOH). Oxygenbarrier films comprising EVOH for packaging food products containing amyoglobin blooming agent can be formed by methods disclosed in U.S. Pat.Nos. 7,018,719; 6,815,023; 6,777,046; 6,511,688; 5,759,648; 5,382,470;and 4,064,296 all of which are incorporated by reference in theirentireties.

Suitable nylons or nylon blends may also be used to impart oxygenbarrier properties. Combinations of barrier materials may also be used.For example, multiple barrier layers of nylon and EVOH are often used toimpart suitable barrier properties in food and meat packaging as areblends of EVOH and nylon. These and other known materials can also beused to form an oxygen barrier layer.

For perishable food packaging, the oxygen (O₂) permeability desirablyshould be minimized. Typical oxygen barrier films will have an O₂permeability of less than about 310 cm³/m² for a 24 hour period at 1atmosphere, 0% relative humidity and 23° C., and preferably less than 75cm³/m², more preferably less than 20 cm³/m². Barrier resins such as PVDCor EVOH in the core layer may be adjusted by blending in compatiblepolymers to vary orientation parameters or the gas permeability e.g. O₂of the films. The thickness of the core layer may also be varied andbeneficially may be from about 0.05 to about 0.30 mils (1.3-7.62microns).

Abuse-Resistant Outer Layer

Since it is seen by the user/consumer, in both the monolayer andmultilayer embodiments of the invention the exterior surface of the filmshould enhance optical properties of the film and may preferably havehigh gloss. Also, it should withstand contact with sharp objects andprovide abrasion resistance, and for these reasons it is often termedthe abuse-resistant layer. This exterior abuse-resistant layer may ormay not also be used as a heat sealable layer. As the exterior surfacelayer of the film, this layer most often is also the exterior layer ofany package, bag, pouch or other container made from the inventive film,and is therefore subject to handling and abuse e.g. from equipmentduring packaging, and from rubbing against other packages and shippingcontainers and storage shelves during transport and storage. Thiscontact causes abrasive forces, stresses and pressures which may abradeaway the film causing defects to printing, diminished opticalcharacteristics or even punctures or breaches in the integrity of thepackage. Therefore the exterior surface layer is typically made frommaterials chosen to be resistant to abrasive and puncture forces andother stresses and abuse which the packaging may encounter during use.The exterior surface layer should be easy to machine (i.e. be easy tofeed through and be manipulated by machines e.g. for conveying,packaging, printing or as part of the film or bag manufacturingprocess). It should also facilitate stretch orientation where a highshrinkage film is desired, particularly at low temperatures such as 90°C. and lower. Suitable stiffness, flexibility, flex crack resistance,modulus, tensile strength, coefficient of friction, printability, andoptical properties are also frequently designed into exterior layers bysuitable choice of materials. This layer may also be chosen to havecharacteristics suitable for creating desired heat seals which may beheat resistance to burn through e.g. by impulse sealers or may be usedas a heat sealing surface in certain package embodiments e.g. usingoverlap seals.

The exterior layer is preferably formed of a similar blend to that ofthe interior layer. In one embodiment at least one and preferably bothinterior and exterior layers utilize polyolefin resins, preferably ablend of (i) EVA, (ii) EAO (such as VLDPE), and (iii) anethylene-hexene-1 copolymer having an mp of 80 to 98° C., preferably 80to 92° C. Each of the three polymers typically comprises 20 to 40 wt. %of the layer. EVA when used in the outer layer preferably has 3% to 18%vinyl acetate content to provide good shrinkability. Blends of EAOs arealso usefully employed in the outer layer.

The exterior layer thickness is typically 0.5 to 1.0 mils. Thinnerlayers may be less effective for abuse resistance, however thickerlayers, though more expensive, may advantageously be used to producefilms having unique highly desirable puncture resistance and/or abuseresistance properties. Heavy gauge films, typically 5 to 7 mils or more,are needed in demanding applications which are usually satisfied by veryexpensive and complex laminated film structures and/or secondarypackaging materials such as bone guards, pads, and overwrap.

In one barrier layer embodiment of this invention an exteriorthermoplastic layer of the enclosing multilayer film is on the oppositeside of a core layer from the interior layer, and in direct contact withthe environment. In a suitable three layer embodiment this exteriorlayer is directly adhered to the core layer which is preferably anoxygen barrier layer.

Intermediate Layers

An intermediate layer is any layer between the exterior layer and theinterior layer and may include oxygen barrier layers, tie layers orlayers having functional attributes useful for the film structure or itsintended uses. Intermediate layers may be used to improve, impart orotherwise modify a multitude of characteristics: e.g. printability fortrap printed structures, shrinkability, orientability, processability,machinability, tensile properties, drape, flexibility, stiffness,modulus, designed delamination, easy opening features, tear properties,strength, elongation, optical, moisture barrier, oxygen or other gasbarrier, radiation selection or barrier e.g. to ultraviolet wavelengths,etc.

Tie Layers

In addition to the exterior layer, the interior layer, and intermediatelayer such as a barrier layer, a multilayer heat shrinkable packagingfilm can further comprise one or more adhesive layers, also known in theart as “tie layers,” which can be selected to promote the adherence ofadjacent layers to one another in a multilayer film and preventundesirable delamination. A multifunctional layer is preferablyformulated to aid in the adherence of one layer to another layer withoutthe need of using separate adhesives by virtue of the compatibility ofthe materials in that layer to the first and second layers. In someembodiments, adhesive layers comprise materials found in both the firstand second layers. The adhesive layer may suitably be less than 10% andpreferably between 2% and 10% of the overall thickness of the multilayerfilm. Adhesive resins are often more expensive than other polymers sothe tie layer thickness is usually kept to a minimum consistent with thedesired effect. In one embodiment, a multilayer film comprises a threelayer structure with an adhesive layer positioned between and in contactwith the first layer and the second layer. In another embodiment, amultilayer film comprises a multilayer structure comprising a firstadhesive layer positioned between and in direct contact with theexterior layer and a core oxygen barrier layer; and preferably andoptionally has a second tie layer between and in direct contact with thesame core oxygen barrier layer and the interior layer to produce a fivelayer film.

Multilayer films can comprise any suitable number of tie or adhesivelayers of any suitable composition. Various adhesive layers areformulated and positioned to provide a desired level of adhesive betweenspecific layers of the film according to the composition of the layerscontacted by the tie layers.

For example adhesive layers in contact with a layer comprising apolyester, such as PET, preferably comprise a suitable blend ofpolyolefins with other adhesive polymers. One preferred component of anadhesive layer in contact with a PET polyester layer is EMAC SP 1330(which reportedly has: a density of 0.948 g/cm³; melt index of 2.0 g/10min.; a melting point of 93° C.; is at softening point of 49° C.; and amethylacrylate (MA) content of 22%).

The interior, exterior, intermediate or tie layers may be formed of anysuitable thermoplastic materials, for example, polyamides, polystyrenes,styrenic copolymers e.g. styrene-butadiene copolymer, polyolefins, andin particular members of the polyethylene family such as LLDPE, VLDPE,HDPE, LDPE, ethylene vinyl ester copolymer or ethylene alkyl acrylatecopolymer, polypropylenes, ethylene-propylene copolymers, ionomers,polybutylenes, alpha-olefin polymers, polyesters, polyurethanes,polyacrylamides, anhydride-modified polymers, acrylate-modifiedpolymers, polylactic acid polymers, or various blends of two or more ofthese materials.

In another embodiment, the exterior, interior and/or one or moreintermediate layers can comprise or consist essentially of a nylon blendcomposition. Preferably, the nylon blend composition comprises at leastan amorphous nylon such as nylon 6I/6T copolymer, in combination with atleast one semi-crystalline nylon homopolymer or copolymer such as nylon6/12, 6/69, 6/66, MXD6, 6, 11, or 12.

In another embodiment of the invention one or more of the exterior,interior and/or one or more intermediate layers comprises at least onepolyester polymer. Preferred polyester polymers comprise aromaticpolyesters and more preferably, are homopolymers or copolymers of poly(ethylene terephthalate) (PET), poly (ethylene naphthalate) and blendsthereof. Suitable polyesters may have an intrinsic viscosity of about0.60 to about 1.2, preferably between 0.60 to 0.80. The polyester may bean aliphatic polyester resin, but is preferably an aromatic polyesterresin. For example, polyester materials can be derived from dicarboxylicacid components, including terephthalic acid and isophthalic acid aspreferred examples, and also dimers of unsaturated aliphatic acids.Examples of a diol component as another component for synthesizing thepolyester may include: polyalkylene glycols, such as ethylene glycol,propylene glycol, tetramethylene glycol, neopentyl glycol, hexamethyleneglycol, diethylene glycol, poly-ethylene glycol and polytetra methyleneoxide glycol; 1,4-cyclohexane-dimethanol, and 2-alkyl-1,3-propanediol.More specifically, examples of dicarboxylic acids constituting thepolyester resin may include: terephthalic acid, isophthalic acid,phthalic acid, 5-t-butylisophthalic acid, naphthalenedicarboxylic acid,diphenyl ether dicarboxylic acid, cyclohexane-dicarboxylic acid, adipicacid, oxalic acid, malonic acid, succinic acid, azelaic acid, sebacicacid, and dimer acids comprising dimers of unsaturated fatty acids.These acids may be used singly or in combination of two or more species.Examples of diols constituting the polyester resin may include: ethyleneglycol, propylene glycol, tetramethylene glycol, neopentyl glycol,hexamethylene glycol, diethylene glycol, polyalkylene glycol,1,4-cyclohexane-dimethanol, 1,4-butanediol, and 2-alkyl-1,3-propanediol. These diols may be used singly or in combination of two or morespecies.

Polyester compositions that comprise an aromatic polyester resincomprising an aromatic dicarboxylic acid component can be preferred insome aspects, including, e.g., polyesters between terephthalic acid (asa dicarboxylic acid) and diols having at most 10 carbon atoms, such aspolyethylene terephthalate and polybutylene terephthalate. Particularlypreferred examples thereof may include: copolyesters obtained byreplacing a portion, preferably at most 30 mol %, more preferably atmost 15 mol %, of the terephthalic acid with another dicarboxylic acid,such as isophthalic acid; copolyesters obtained by replacing a portionof the diol component such as ethylene glycol with another diol, such as1,4-cyclohexane-dimethanol (e.g., “Voridian 9921”, made by Voridiandivision of Eastman Chemical Co.); and polyester-polyether copolymerscomprising the polyester as a predominant component (e.g.,polyester-ether between a dicarboxylic acid component principallycomprising terephthalic acid or/and its ester derivative and a diolcomponent principally comprising tetramethylene glycol andtetramethylene oxide glycol, preferably containing the polytetramethylene oxide glycol residue in a proportion of 10-15 wt. %). It isalso possible to use two or more different polyester resins in mixture.Examples of preferred polyesters are available under the trademarksVoridian 9663, Voridian 9921 and EASTAR® Copolyester 6763, all fromEastman Chemical Company, Kingsport, Tenn., U.S.A. U.S. Pat. No.6,964,816 to Schell et al. and U.S. Pat. No. 6,699,549 to Ueyama et al.,which are incorporated herein by reference in their entireties, disclosemultilayer structures comprising a polyester layer, and a polyamidelayer.

Optional Additives to Layers

Various additives may be included in the polymers utilized in one ormore of the exterior, interior and intermediate or tie layers of foodpackaging comprising the same. For example, a layer may be coated withan anti-block powder. Also, conventional anti-oxidants, antiblockadditives, polymeric plasticizers, acid, moisture or gas (such asoxygen) scavengers, slip agents, colorants, dyes, pigments, organolepticagents may be added to one or more film layers of the film or it may befree from such added ingredients. If the exterior layer is coronatreated, preferably no slip agent will be used, but it will contain orbe coated with an anti-block powder or agent such as silica or starch.Processing aides are typically used in amounts less than 10%, less than7% and preferably less than 5% of the layer weight. A preferredprocessing aid for use in the outer layer of the film includes one ormore of fluoroelastomers, stearamides, erucamides, and silicates.

Preferred films may also provide a beneficial combination of one or moreor all of the properties including low haze, high gloss, high shrinkagevalues at 90° C. or less, good machinability, good mechanical strengthand good barrier properties including high barriers to oxygen and waterpermeability.

Methods of Manufacture

The inventive monolayer or multilayer film may be made by conventionalprocesses which are modified to provide for inclusion of a myoglobinblooming agent. These processes to produce flexible films may includee.g. cast or blown film processes, but will include a stretching ororientation process under conditions to produce a film which isuniaxially or biaxially heat shrinkable at 90° C. or less. In thepresent invention a heat shrinkable film is provided to be heat shrunkenabout a food product such as meat to form a package. Thus, a heat shrunkfilm pouch will advantageously cling to the packaged foodstuff tofacilitate transfer of the myoglobin blooming agent. Non-shrink bagshave an undesirable wrinkled appearance with excess film forming “ears”,tabs and other protrusions, and internal forces e.g. from whole birdpoultry wings and legs or purge of internal juices or gases may causeloss of contact with food product surfaces which are undesirable. Oncethe film separates from the enclosed article surface, the myoglobinblooming agent is not in contact and oxygen may also come into contactwith the article surface and either event may result in an undesirablynonuniform color or other product defects.

The monolayer and multilayer films may be manufactured by known methodsin the art as modified as described herein for inclusion of a myoglobinblooming agent. Descriptions of suitable film manufacturing andorientation processes are disclosed in e.g. U.S. Pat. Nos. 5,759,648,6,316,067 and 6,773,820, and U.S. Patent Application Publication No.2004/0166262 (Busche et al.), entitled, “Easy open heat-shrinkablepackaging,” all of which are incorporated herein by reference in theirentireties.

Various manufacturing methods may be used as will be apparent to thoseskilled in the art in view of the present teaching. For example, U.S.Pat. No. 4,448,792 (Schirmer) discloses a method comprising the steps ofcoextrusion, biaxial orientation and irradiation, and U.S. Pat. No.3,741,253 (Brax et al.) discloses a method of extrusion, irradiation,extrusion lamination/coating and biaxial orientation, and both patentsare hereby incorporated by reference in their entireties.

In a preferred process for making films, the resins and any additivesare introduced to an extruder (generally one extruder per layer) wherethe resins are melt plastified by heating and then are transferred to anextrusion (or coextrusion) die for formation into a tube. Extruder anddie temperatures will generally depend upon the particular resin orresin containing mixtures being processed and suitable temperatureranges for commercially available resins are generally known in the art,or are provided in technical bulletins made available by resinmanufacturers. Processing temperatures may vary depending upon otherprocess parameters chosen. However, variations are expected which maydepend upon such factors as variation of polymer resin selection, use ofother resins e.g. by blending or in separate layers in the multilayerfilm, the manufacturing process used and particular equipment and otherprocess parameters utilized. Actual process parameters including processtemperatures are expected to be set by one skilled in the art withoutundue experimentation in view of the present disclosure.

As generally recognized in the art, resin properties may be furthermodified by blending two or more resins together and it is contemplatedthat various resins including e.g. homopolymers and copolymers maycomprise or be blended into individual layers of the multilayer film oradded as additional layers, such resins include polyolefins such asethylene-unsaturated ester copolymer resins, especially vinyl estercopolymers such as EVAs, or other ester polymers, very low densitypolyethylene (VLDPE), linear low density polyethylene (LLDPE), lowdensity polyethylene (LDPE), high density polyethylene (HDPE), ionomers,polypropylenes, or blends thereof. Other polymers that may be includedas separate layers or in combination include polyamides such as nylon,PVDC, EVOH, and PET. These resins and others may be mixed by well knownmethods using commercially available tumblers, mixers or blenders.

Also, if desired, well known additives such as anti-oxidants, processingaids, slip agents, antiblocking and antifogging agents, pigments, etc.,and mixtures thereof may be incorporated into the film. For example, themyoglobin blooming agent containing layer and/or other layers mayfurther comprise an antioxidant, a slip agent, an antiblock agent, acolorant, a color enhancer, a flavorant, an odorant, an organolepticagent, a coefficient of friction modifying agent, a lubricant, asurfactant, an encapsulating agent, an oxygen scavenger, a pH modifyingagent, a film forming agent, an emulsifier, a polyphosphate, ahumectant, a drying agent, an antimicrobial agent, a chelating agent, abinder, a starch, a polysaccharide, a stabilizer, a buffer, aphospholipid, an oil, a fat, a protein, a polysaccharide, a transferagent, or a combination thereof. Examples of particular compositionsthat may be added include: α-tocopherol; alcohol; annatto; ascorbicacid; beet powder; BHA; BHT; bixin; caramel; carmine; carotenoidpigment; casein; cochineal; cyclodextrin; dextrin; erucamide;ethoxylated mondiglycerides; fluoroelastomer; food grade oil; glycerine;lecithin; liquid smoke; nisin; norbixin; pediocin; polysorbate;potassium chloride; rosemary extract; shellac; sodium chloride; sodiumerythorbate; starch; trisodium polyphosphate; turmeric; water; watersoluble cellulose ether; and zein.

Various polymer modifiers may be incorporated for the purpose ofimproving toughness, orientability, extensibility and/or otherproperties of the film. Other modifiers which may be added includemodifiers which improve low temperature toughness or impact strength andmodifiers which reduce modulus or stiffness. Exemplary modifiers includestyrene-butadiene, styrene-isoprene, and ethylene-propylene copolymers.

As used herein, the phrase “machine direction”, herein abbreviated “MD”,refers to a direction “along the length” of the film, i.e., in thedirection of the film as the film is formed during extrusion and/orcoating. As used herein, the phrase “transverse direction”, hereinabbreviated “TD”, refers to a direction across the film, perpendicularto the machine or longitudinal direction.

The films are made heat shrinkable, preferably by stretch orientation.Stretch orientation may be accomplished by various known methods e.g.machine direction (MD) orientation is preferably accomplished with theuse of sets of nip rolls rotating at different speeds to stretch or drawthe film, sheet or tube in the machine direction thereby causing machinedirection elongation which is set by cooling. Other methods includetentering which is commonly employed to orient sheets, or the well-knowntrapped bubble or double bubble technique for orienting tubes as forexample described in U.S. Pat. No. 3,456,044 (Pahlke) which is herebyincorporated by reference in its entirety. In the bubble technique, anextruded primary tube leaving a tubular extrusion die is cooled,collapsed and then preferably oriented by reheating and inflating toform an expanded secondary bubble, which is again cooled and collapsed.This collapsed stretched film may be wound on a reel as a tube or slitinto sheets or webs and wound, or it may be further processed e.g. byannealing or irradiation as described below.

Preferred films are biaxially stretched. Transverse direction (TD)orientation is accomplished by the above noted inflation to radiallyexpand the heated film which is cooled to set the film in an expandedform or by pulling the film in the transverse direction duringtentering. Orientation may be in either or both directions. Preferably,a primary tube is simultaneously biaxially stretched radially(transversely) and longitudinally (machine direction) to produce amultilayer film which is heat shrinkable at temperatures below themelting points of the major polymeric components, e.g., at 90° C. orlower. The stretch ratio during orientation should be sufficient toprovide a film with a total thickness of 10 mil or less and preferredfilms will be under 5 mil and typically between about 1.0 and 4.0 mils.The MD stretch ratio is typically 2½-6 and the TD stretch ratio is alsotypically 2½-6. An overall or total stretch ratio (MD stretch multipliedby TD stretch) of about 6¼×-36× is suitable.

Axially stretched, especially biaxially stretched, films which are “heatshrinkable” as that term is used herein have at least 10% unrestrainedshrinkage at 90° C. in at least one of the machine direction (MD) ortransverse direction (TD). Preferably for biaxially stretched filmsthere is at least 10% shrink in each of the MD and TD for a total freeshrink of at least 20%. One or more of the film layers may be orientedeither uniaxially or biaxially by axial stretching at temperatures lowenough to produce low temperature, high shrink multilayer films e.g. at85° C., 80° C., 74° C. or lower. Such heat shrinkable multilayer filmswill have at least 10% shrink in at least one direction at 90° C., butbeneficially may have at least 10% shrink at one or more of the lowertemperatures in at least one, but preferably both MD and TD directionsand preferably at least 15% (more preferably at least about 20%) in atleast one direction at 85, 80, or 74° C.

The general annealing process by which biaxially stretched heatshrinkable films are heated under controlled tension to reduce oreliminate shrinkage values is well known in the art. If desired, filmsmay be annealed to produce lower shrinkage values as desired for theparticular temperature.

Optionally, films of the present invention may be subject to a varietyof irradiative treatments. In the irradiation process, the film issubjected to an energetic radiation treatment, such as corona discharge,plasma, flame, ultraviolet, X-ray, gamma ray, beta ray, and high energyelectron treatment. These irradiative treatments may be performed for avariety of reasons including e.g. modifying surface characteristics toimprove surface adhesion to a variety of substances such as meat orprinting ink, or to improve internal layer adhesion to ameliorateintralayer adhesion and avoid undesirable delamination. An importantknown use of irradiation is to induce cross-linking between molecules ofthe irradiated material. The irradiation of polymeric films to inducefavorable properties such as crosslinking is well known in the art andis disclosed in U.S. Pat. No. 4,737,391 (Lustig et al) and U.S. Pat. No.4,064,296 (Bornstein et al.), which are hereby incorporated by referencein their entireties. Bornstein et al. discloses the use of ionizingradiation for crosslinking the polymer present in the film. In somepreferred embodiments, it is preferred to crosslink the entire film tobroaden the heat sealing range. This is preferably done by irradiationwith an electron beam at dosage levels of at least about 2 megarads (MR)and preferably in the range of 3 to 8 MR, although higher dosages may beemployed. Irradiation may be done on the primary tube, with or withoutadditional layers being coated thereon, or after biaxial orientation.The latter, called post-irradiation, is described in U.S. Pat. No.4,737,391 (Lustig et al.). An advantage of post-irradiation is that arelatively thin film is treated instead of the relatively thick primarytube, thereby reducing the power requirement for a given treatmentlevel.

Alternatively, crosslinking may be achieved by addition of a chemicalcrosslinking agent or by use of irradiation in combination with acrosslinking modifier added to one or more of the layers, as for exampledescribed in U.S. Pat. No. 5,055,328 (Evert et al.).

Fundamental to the present invention is inclusion of a myoglobinblooming agent with a heat shrinkable oxygen barrier film. The packagingfilms can have any suitable structure, but it is essential that themyoglobin blooming agent be on, or in, or able to migrate to, a foodcontact portion of the heat shrinkable film.

Whether the myoglobin blooming agent is coated on or incorporated withinan interior food contact layer, it may be applied by any suitablemethod, e.g. as described above, including dry or wet spraying, dusting,blending, coating e.g. with transfer rollers, slugging, inclusion in amasterbatch, printing, etc. The myoglobin blooming agent is preferablyevenly dispersed over the contact surface of the layer and/or throughoutthe entire layer to enable any length of film incorporating the layer toinclude approximately similar amounts of the compound Within the sealinglayer for a uniform transfer to meat via surface contact.

Where the myoglobin blooming agent is coated on the film food contactlayer surface it may be conveniently applied at various times. Forexample, the agent may be applied to the meat surface e.g. by dipping orspraying just before packaging, or during a bag making operation with orwithout admixture with starch used as a means to facilitate subsequentbag opening. It may be applied during winding operations attendant toslitting operations or during pouch making or tube making. It may beapplied before or after irradiative treatments. It may be applied withor in place of starch utilizing electron beam irradiation and/or coronatreatment as further described in U.S. Pat. No. 5,407,611 (Wilhoit etal.) which is hereby incorporated by reference. Agents such as nitriteor nitrate are soluble in water or alcohol, and solutions of myoglobinblooming agent may be coated on films either alone or incorporated withother agents such as film forming and/or wetting agents or othermaterials such as zein, casein, dextrin, starch, or shellac, etc. usede.g. with respect to transferring bixin as described in U.S. Pat. No.6,143,344 (Jon et al) which is hereby incorporated by reference. Theagent may also be applied in an aqueous solution to a film whose foodcontact surface has been modified to be hydrophilic or adapted orotherwise modified to adsorb or absorb water or oil based liquidscontaining a myoglobin blooming agent. According to the presentinvention in one aspect transferable modifier-containing films may beutilized to transfer myoglobin blooming agents using e.g. films having afood contact layer formulation suitable for effecting transfer asdescribed in U.S. Pat. No. 5,288,532 (Juhl et al); U.S. Pat. No.5,374,457 (Juhl et al); U.S. Pat. No. 5,382,391 (Juhl et al); and U.S.Pat. No. 6,667,082 (Bamore et al) which are all hereby incorporated byreference.

Where the myoglobin blooming agent is incorporated within the interiorlayer, it may be added to a base polymer before or during extrusion ofthe film. The base polymer may be any suitable polymer e.g. a polyolefinsuch as a polyethylene, and may be very low density polyethylene(VLDPE), linear law density polyethylene (LLDPE), low densitypolyethylene (LDPE), EVA, polypropylene, ionomer, nylon, PVDC, PET, etc.Melt blending is a suitable method of mixing the base polymer and themyoglobin blooming compound. The individual component materials may becombined in a high intensity mixing device such as an extruder. The basepolymer is melted to form a viscous liquid or “melt.” The myoglobinblooming compound may be combined with the polymer before, during, orafter melting. The high intensity mixing device is used to attempt touniformly disperse the myoglobin blooming compound within the basepolymer. The quality and functionality of the dispersed agent can dependupon the choice of myoglobin blooming agent, the composition of the basepolymer and the mixing device. It is desirable to achieve good mixingfor uniform dispersion of the myoglobin blooming agent within the melt;the presence of poorly wetted particle agglomerations is undesirable. Itmay be desirable to include additives in the blend such as e.g.anti-oxidants, anti-block or slip agents.

The myoglobin blooming agent may be either directly added to the basepolymer or provided in a solution such as an aqueous or oil basedsolution that is added to the polymer either before or during the meltstate of the polymer. For direct addition of a solid, granular orparticulate agent grinding the solid agent to produce smaller particlesis expected to provide a more uniform dispersion. It is expected thatfor a water soluble material, providing the myoglobin blooming agent asan aqueous solution may provide better dispersion of the compound withinthe polymer relative to addition of undissolved agent. An aqueoussolution may be prepared from a water soluble myoglobin blooming agentsuch as sodium nitrite, preferably close to the saturation concentrationof the aqueous solution and may e.g. include between about 20 wt % andabout 42 wt % of a compound which acts as a myoglobin blooming agent.This aqueous solution may be directly introduced into a polymer melte.g. in an extruder heated to a temperature above 300° F. to facilitatemixing to form a blend. If added as a solution provision should be madefor venting water vapor from the extruder. The polymer blend containinga myoglobin blooming agent may be either extruded into pellets, ordirectly as a film.

The myoglobin blooming agent may be mixed with a carrier resin or basepolymer to form a masterbatch. Pellets from the masterbatch may beconvenient for subsequent use in fabricating articles. Pellets from themasterbatch may then be mixed with the base polymer or another polymerduring a film forming process.

When used to create a masterbatch, a sufficient amount of the solutionmay be introduced into the polymer melt to obtain a blend having a highconcentration of myoglobin blooming agent e.g. between about 2 wt % andabout 10 wt % myoglobin blooming compound, and preferably between about4 wt % and about 6 wt %.

Monolayer Barrier Films

In one embodiment of the invention, monolayer heat shrinkable, oxygenbarrier packaging films are provided which comprise a food contact layerincluding a myoglobin blooming agent. The agent may either be coatedonto the surface of the monolayer film or it may be incorporated thereine.g. during the extrusion process. A nylon blend of an amorphous nylonsuch as nylon 6I,6T with one or more semicrystalline nylons such ascopolymers nylon 6/12, 6/66, 6/69 and/or homopolymers nylon 6, 11, 12,MXD6 and 66 may be made into a heat shrinkable film as disclosed e.g. inU.S. Pat. No. 5,344,679 (Vicik) which is hereby incorporated byreference in its entirety. Such film has both heat shrinkability andprovides an oxygen barrier and may have a myoglobin blooming agentcoated on or incorporated therein.

Multilayer Barrier Films

Multilayer oxygen barrier, heat shrinkable films having a myoglobinblooming agent that contacts a packaged meat product surface candesirably promote, preserve or enhance a desirable myoglobin-mitigatedred color.

In one aspect of the embodiment, a myoglobin blooming agent is includedin the food contact layer, which is preferably a sealant layer.Multilayer films advantageously may utilize one or more additionallayers to provide beneficial film properties. Multilayer films haveincreased flexibility of application over monolayer films in thatspecific layers may be provided to incorporate specific features.Sometimes materials which may be unsuitable alone may be advantageouslyemployed in a multilayer construction. For example, EVOH has oxygenbarrier properties which are very sensitive to moisture anddetrimentally impacted thereby, but when protected from contact withmoisture by adjacent moisture barrier layers EVOH may provide a filmhaving an excellent oxygen barrier. Oxygen barrier layers may bepositioned between an abrasion or abuse resistant layer and a foodcontact layer containing myoglobin blooming agent to protect the oxygenbarrier and permit thinner oxygen barrier layers to be used. Where EVOHbarrier materials are used, it is contemplated that apolyamide-containing layer may optionally be in contact with the EVOHmaterial. Non-limiting examples of various preferred multilayer filmconfigurations include the following:

Abuse Resistant (Exterior)/O₂ Barrier/Food Contact & Sealant (Interior);Abuse Resistant (Exterior)/Core/O₂ Barrier/Core/Sealant (Interior);Abuse Resistant (Exterior)/Tie/Core/O₂ Barrier/Core/Sealant (Interior);Abuse Resistant (Exterior)/Tie/Core/O₂ Barrier/Core/Tie/Sealant(Interior); Abuse Resistant (Exterior)/Core/Tie/O₂Barrier/Tie/Core/Sealant (Interior); Abuse Resistant (Exterior)/Tie/O₂Barrier/Tie/Sealant (Interior); Abuse Resistant (Exterior)/Nylon Core/O₂Barrier/Core/Sealant (Interior); Abuse Resistant (Exterior)/Tie/Core/O₂Barrier/Nylon Core/Sealant (Interior); and Abuse Resistant(Exterior)/Tie/Core/O₂ Barrier/Nylon Core/Tie/Sealant (Interior)

Some embodiments provide a 3, 4, 5, 6, 7, 8, 9, or more layer coextrudedfilm with desirable levels of abuse resistance, oxygen barrier and heatshrinkability in a multilayer film structure.

Referring now to the drawings, FIG. 1 discloses an example of athree-layer film structure embodiment of the present invention generallydesignated at reference numeral 10. This embodiment is directed to amultilayer composite comprising an outer layer 12 that is an exteriorlayer 102 comprising a material such as a polyolefin, PET or a nyloncomposition, and an outer layer 14 that is a sealant layer 122, eachjoined to opposite sides of a core tie oxygen barrier layer 112comprising e.g. PVDC. The sealant layer 122 comprises a myoglobinblooming agent such as sodium nitrite or sodium nitrate or blendsthereof. The multilayer heat shrinkable film 10 is designed to be usedin the packaging of food products and can be used for a casing, bag,pouch or to overwrap a tray or in a form shrink or other vacuum package.

Referring now to FIG. 2, a cross section of an example of a five layerheat-shrinkable oxygen barrier film is depicted with film 20 having anexterior surface layer 22 that is an abuse resistant layer 102 joined bya first tie layer 112 to a core and barrier polyamide layer 26comprising one or more nylon polymers 104, the other side of core layer26 is joined by a second tie layer 114 to an interior surface layer 24which is a sealant layer 122 comprising a myoglobin blooming agent.

Placement of one or more core nylon layers in contact with an EVOHoxygen barrier layer can provide multilayer free shrink films with ahigher total free shrink or improved processability. In certainembodiments nylon may be blended with EVOH or may be included asadjacent layers e.g. when EVOH oxygen barrier materials have an ethylenecontent of about 44 mol % or less, at least one and preferably twopolyamide core layers may be included in contact with the EVOH layer tofacilitate processing.

Referring now to FIG. 3, a cross-section of an example of a seven layerfilm 30 is depicted. Film 30 may comprise an exterior layer 32 that isan abuse resistant layer 102 having high gloss and good printabilitywhich is in direct contact with a first tie layer 112 and connectedthereby to a first core polyamide layer 36 comprising one or more nylonpolymers 104. Nylon layer 36 is in direct contact with an oxygen barrierlayer 35. Similarly, the other side of the oxygen barrier layer 35comprising EVOH 130, is joined to a second core polyamide layer 38comprising one or more nylon polymers 104, the other side of which isjoined to a second tie layer 116. The interior layer 34 is a foodcontact layer 122 which may also be heat sealable and which comprises amyoglobin blooming agent. The food contact sealant layer is joined tothe second tie layer 116. Preferably all seven layers are coextruded,but they also be formed by lamination e.g. coating lamination or acombination thereof.

First tie layer 112 promotes or provides adhesion between an abuseresistant layer 102 that is an exterior layer 32, and a core polyamidelayer 104. Similarly, tie layer 116 promotes or provides adhesionbetween a second polyamide layer 38 and a food contact layer 122 that isan interior layer 34. Tie layers 112, and 116 may be identical ordifferent from each other, and may include a wide range ofanhydride/grafted polyolefins including those based on ethylene vinylacetate copolymer, polypropylene, low density polypropylene, linear lowdensity polypropylene, and very low density polyethylene. Preferably,the compositions of tie layers are based on linear low densitypolyethylene, or plastomers such as metallocene catalyzed polyethylene.Exemplary tie layer resins are manufactured by Equistar Chemical Companyunder the trade name Plexar®.

Some embodiments provide a multilayer, heat-shrinkable, easy opening,oxygen barrier casing, pouch, bag or food package formed from multilayerfilms that preferably are at least partially coextruded and morepreferably fully coextruded.

Referring now to FIG. 4 a cross-sectional view is depicted of an exampleof a five layer film 40 for use in an easy to peel open, heatshrinkable, oxygen barrier package comprising an exterior surface layer42 that is preferably a heat sealable polyolefin layer 202 joined to apeelable tie layer 212 which preferably comprises a blend ofpolybutylene and polyethylene. The opposite side of the peelable tielayer 212 is joined to an intermediate (core) layer 45 preferablycomprising a polyolefin 230 such as a blend of polyethylene and EVA, theopposite side of which is joined to an oxygen barrier layer 214 whichpreferably may be a PVDC blend. The interior myoglobin blooming agentcontaining surface layer 44 is a heat sealable layer 222 that is joinedto the oxygen barrier layer 214. This embodiment provides an easy topeel open version of the inventive film and package. Additionaldescription of such easy to peel open heat shrinkable films may be foundin U.S. Patent Publication No. 2004/0166262 (Busche et al) which ishereby incorporated by reference.

Optionally, in another embodiment of the invention the core oxygenbarrier layer 214 of the embodiment of FIG. 4 is replaced with a threelayer structure of a first tie layer and a second tie layer on opposingsides of an EVOH oxygen barrier layer to provide a 7 layer film.

In yet another embodiment of the invention the core oxygen barrier layer214 of the embodiment of FIG. 4 is replaced with a five layer structurehaving an EVOH oxygen barrier layer with first and second nylon layerson opposing sides thereof with a first tie layer in direct contact withthe first nylon layer and a second tie layer in direct contact with thesecond nylon layer to provide a 9 layer heat shrinkable film.

A packaging film according to the present invention has a free shrinkvalue at 90° C. of at least 10% in at least one of the machine directionor transverse direction. The monolayer and multilayer packaging filmspreferably have a free shrink of at least 30%, more preferably at least40% at 90° C. in the machine direction, the transverse direction, or inboth the machine direction and the transverse direction. Advantageously,in certain embodiments the myoglobin blooming agent containing packagingfilms have a free shrink in the machine direction of about 30%, 35%,40%, 45%, 50%, 55%, 60% or greater, including any increment of 1%therebetween, measured at 90° C. and preferably at lower temperaturessuch as 85, 80 or 74° C. Advantageously, in certain embodiments themyoglobin blooming agent containing packaging films have a free shrinkin the transverse direction of about 30%, 35%, 40%, 45%, 50%, 55%, 60%or greater, including any increment of 1% therebetween, measured at 90°C. and preferably at lower temperatures such as 85, 80 or 74° C.Beneficially, packaging films may have a free shrink of at least 40% intwo directions. For certain embodiments it is preferred that packagingfilms have a free shrink of at least 40% in the machine direction and atleast 50% in the transverse direction.

Heat-shrinkable films have a total free shrink at 90° C. of at least10%, and more preferably at least about 20, 30, 40, 50, 60, 70% orgreater. Desirably, in certain embodiments heat shrinkable, oxygenbarrier, packaging films according to the present invention may have atotal free shrink of at least about 50%, 80%, 85%, 90%, 95%, 100%, 105%,110% or higher measured at 90° C.

Examples of food packaging film products that can be combined with amyoglobin blooming agent in accordance with the teachings include U.S.Pat. Nos. 6,514,583; 4,801,486; Re35,285; 4,755,403; 6,299,984;6,221,470; 6,858,275; 4,755,419; 5,834,077; 6,610,392; 6,287,613;6,074,715; 6,511,568; 6,753,054; 4,610,914; 4,457,960; 6,749,910;6,815,023; 5,593,747; 5,382,470; and 6,565,985, as well as publishedU.S. Patent Application No. US 2005/0129969, which are incorporatedherein by reference. Preferably, the myoglobin blooming agent isincluded in the food contact layer of the packaging film, which ispreferably a heat sealable layer.

In one aspect of the invention, heat shrinkable films may be providedthat comprise a myoglobin blooming agent in combination with ahomogeneous alpha-olefin copolymer. For example, the homogenousalpha-olefin copolymer can be an ethylene/C₆₋₁₀ copolymer disclosed inU.S. Pat. No. 6,514,583 (Ahlgren et al.) including a heat-shrinkablefilm comprising homogeneous linear ethylene/C₃₋₁₂ alpha-olefincopolymer, the heat-shrinkable film having an impact strength of atleast 30 pounds and a total free shrink, at 185° F., of at least 30percent.

In another aspect of the invention, other known multilayer thermoplasticflexible packaging films can be combined with a myoglobin bloomingagent. For example, a myoglobin blooming agent can be combined with thepackaging films described in U.S. Pat. No. Re. 35,285 or U.S. Pat. No.4,801,486 (Quacquarella et al.) which are incorporated herein byreference. The multilayer thermoplastic packaging films can comprise amyoglobin blooming agent in one or more of the surface layers: (a) afirst surface layer which is a heat sealing surface, comprising: acopolymer of ethylene and an alpha-olefin having 4 to 8 carbon atoms permolecule, and comprising 90% to 75% ethylene and 10% to 25% alpha-olefinhaving 4 to 8 carbon molecules and a density of less than 915 kg/m³;and/or (b) a second surface layer, comprising a polymer selected fromthe group consisting of amide polymers, ethylene vinyl acetatecopolymers, the copolymer of the first surface layer, and ionomers.

Alternatively, a myoglobin blooming agent can be combined with one ormore surface layers of the packaging films described in U.S. Pat. No.6,299,984 (Forloni) which is incorporated herein by reference.

In another aspect of the invention, patches adapted for use incombination with a heat-shrinkable bag, e.g. as disclosed in U.S. Pat.No. 4,755,403 to Ferguson, can be combined with a myoglobin bloomingagent.

A monolayer or multilayer patch can comprise a myoglobin blooming agentin at least one layer of a protective heat shrinkable ornonheatshrinkable patch in combination with a biaxially heat shrinkablebag. The patch is preferably biaxially heat shrinkable, and may beadhered to the bag using adhesives, corona treatment or by other meanswell known in the art. A patch may be on the inside, outside or bothsides of the bag, but a patch comprising a myoglobin blooming agentshould be positioned for contact with a myoglobin containing foodproduct such as meat (which also includes meat bone), and the patch willshrink with the bag, thereby reducing the tendency of the patch todelaminate from the bag, or it may optionally be a nonshrink film thatis adapted to otherwise conform to a shrinking bag. Most preferably, theinterior surface food contact layer of the patch may further comprisethe myoglobin blooming agent, such as a nitrite, nitrate or Fremy'ssalt, in combination with a suitable food contact polymer. For example,the inner layer can comprise an ethylene-vinyl acetate copolymer e.g.having 20% to 35% by weight vinyl acetate content, and e.g. includingabout 0.1-5% of the myoglobin blooming agent in a food contact surface.

Methods of Packaging

In another aspect of the invention, methods of packaging amyoglobin-containing food product are provided. Suitable meat productsare preferably fresh meat, but may also be enhanced or processed meats,such as the meat products described above.

The meat product is desirably a fresh meat product provided within aperiod of time postmortem to provide a desired level of freshness andsafety. Preferably, a food product comprising myoglobin is provided forpackaging less than 20 days post-mortem, more preferably less than 14,12, 10, 6, 5, 4, 3, 2, or 1 day. Typically, the food product is a freshmeat provided between about 2 days and 14 days post-mortem, and morepreferably between about 2 days and about 12 days.

Fresh meat is typically packaged in a moist state. Typically, meatcomprises moisture (water), protein and fat. Fresh meat can includeabout 60% to about 80% moisture content, with lean meats typicallyhaving higher moisture content. Fresh meat products such as ground beef,chicken and pork often have a moisture content of about 68% to about75%, depending on the fat content of the meat (meats with higher fatcontents tend to have lower moisture content and vice versa). Curedmeats often have higher moisture content due to injection withwater-based preserving compounds. Sausage products may have a lowermoisture content. For example, pork sausage may have a moisture contentof about 40% or higher. Preferably, the packaged meat product can have amoisture content of at least about 5%, 10%, 15%, 20%, 30%, 40%, 50%,60%, 70%, 80% or more.

The meat product may be packaged in a suitable food package and/orpackaging film, such as the packages and films described herein.Preferably, the meat product is contacted by the myoglobin bloomingagent containing food contact surface of the packaging. The myoglobinblooming agent (MBA) preferably will contact the meat surface in anamount sufficient to produce a desired red color which preferably doesnot penetrate to an undesirable depth of the food thickness underreduced oxygen conditions (this color may take awhile to develop e.g. 1to 5 days). Beneficially the MBA may be present on the film food contactsurface (or on the myoglobin food surface) in an amount of from about0.05 to 3 to 5 to 10 μmoles/in² and in increments of 0.1 μmole thereof.Greater or lesser amounts of MBA may be used and the color intensity maythereby be varied depending upon the relative presence or absence ofmyoglobin. The food contact layer preferably has between about 0.001mg/in² and about 0.900 mg/in² of a myoglobin blooming agent such asNaNO₂. Also the packaging should maintain the food product in a reducedoxygen package environment having a reduced gaseous oxygen partialpressure. The reduced oxygen package may comprise an oxygen barrierlayer having an oxygen transmission rate of less than about 310, 200,100, 75, 50, 40, 30, 20 or 10 cm³/m²/24 hours measured at 0% relativehumidity and 23° C. Preferably, the oxygen barrier layer has an oxygentransmission rate of less than about 310 cm³/m²/24 hours measured at 0%relative humidity and 23° C., more preferably less than about 75cm³/m²/24 hours, and most preferably less than about 20 cm³/m²/24 hours.

In many packaging applications, such as vacuum packaging, heatshrinkable food packaging films are desirable. Heat shrinkable bags andpouches can be made with heat sealable layers. A typical food packagingpouch can include three sides heat sealed by the pouch manufacturerleaving one open side to allow product insertion. Flexible food packagecontainers such as bags or pouches may be made by transversely cuttingtubular stock of monolayer or multilayer film and cutting off the tubeportion containing the sealed end; by making multiple spaced aparttransverse seals on tubular stock and cutting open the side of the tube;by superimposing flat sheets of film and sealing on three sides; or byfolding a flat sheet and sealing on two sides. A processor may theninsert e.g. fresh, frozen, hard chilled, thawed, raw, enhanced, cured orprocessed meat, ham, poultry, primal or subprimal meat cuts, groundbeef, or other myoglobin containing products, making a final seal tohermetically enclose the product in the bag. This final seal preferablyfollows gas evacuation (e.g. by vacuum removal). Flexible food packagingcontainers such as bags or pouches can be made by transversely sealingtubular stock of monolayer or multilayer film and cutting off the tubeportion containing the sealed end; by making two spaced apart transverseseals on tubular stock and cutting open the side of the tube; bysuperimposing flat sheets of film and sealing on three sides; or byfolding a flat sheet and sealing two sides. The final seal afterinsertion of a food product may be a clip, but is usually a heat sealsimilar to the initial seals produced by the bag manufacturer althoughthe actual heat sealing equipment may vary. Hot bar and impulse sealersare commonly used to make heat seals.

The inventive film may also be used in embodiments employing trays e.g.as a lidding film or tray overwrap. Equipment such as tray sealers thatare made by Ossid Corporation of Rocky Mount, N.C., USA or ULMAPackaging, Inc. of Woodstock, Ga., USA may be used to package poultrysuch as chicken or other meats. Tray packaging may optionally involvereplacement of the gaseous environment within the package by one or moregases to provide some advantage such as to assist product preservation,but to enjoy preferred benefits of the present invention at least aportion of the oxygen barrier film should be in contact with a foodsurface under reduced oxygen conditions to fix color in that contactarea in a manner where a consumer or potential purchaser may view thecolor fixed meat surface through a transparent portion of the film.

Suitably at least 10%, preferably at least 20% and more preferably atleast 30% or 50% or more of the surface of the oxygen barrier film istransparent to allow visual perception of food color therethrough afterpackaging. Meats having a bright red color are believed to be morevisible, and have greater definition to distinguish the meat's physicaltopography, texture, and color variation e.g. such as that found inmarbling. It is further believed, without wishing to be bound by thebelief, that the whites of meat components such as fats, skin and whitemuscle fibers are enhanced by having proximate myoglobin bound bymyoglobin blooming agents which fix a bright red color as opposed topurplish, bluish or brownish colors. Thus, the whites appear whiter inpoultry and other meats including beef and pork. This in turn causesconsumers to have a perception of greater clarity of the meat surfacewhich increases consumer confidence in their purchase over meats havingless visible surface characteristics.

In an embodiment of the invention a method of manufacturing a vacuumpackage of fresh meat may be provided which comprises:

-   -   a) supplying a container comprising a heat shrinkable film        having a layer comprising a myoglobin blooming agent and wherein        the film is substantially impermeable to oxygen;    -   b) placing a retail cut of fresh meat within the container;    -   c) removing the atmosphere within the container;    -   d) causing transparent portion of the film to make direct        contact with at least a portion of the meat surface;    -   e) hermetically sealing the container to enclose the fresh meat        and prevent contact of oxygen from outside the container        therewith;    -   f) shrinking the film to provide a compact package having a        sufficiently reduced internal oxygen level to promote a meat        surface favoring deoxymyoglobin or metmyoglobin and the        corresponding purple and brown colorations associated therewith        over formation of oxymyoglobin; and    -   g) storing the package under refrigeration conditions for a        sufficient time to permit the reducing activity of the enclosed        meat to favor nitroxymyoglobin formation on the meat surface to        an extent whereby a corresponding red color associated therewith        is formed to produce a visibly red meat surface.

Variations of the above embodiment may utilize the wide selection ofMBAs, polymers, films, attributes and parameters disclosed herein aswill be recognized by one skilled in the art in view of the presentteaching.

Food Packaging

In another embodiment, food packages are provided that comprisemyoglobin-containing food product such as fresh meat. The food packagespreferably include a heat shrinkable oxygen barrier packaging filmcomprising a myoglobin blooming agent as described above, but may alsoinclude heat shrinkable films in combination with a food product whichhas been surface coated with a myoglobin blooming agent prior topackaging.

In some embodiments, the heat-shrinkable food package comprises a heatsealant layer positioned at or near the interior surface of the package,for example as an interior layer. The sealant layers of the heatshrinkable food package are described above.

The heat-shrinkable food packages further comprise an oxygen barrierlayer as part of the film forming the food package. The oxygen barrierlayer can comprise any suitable material and in a multilayer embodimentis preferably positioned between the abuse resistant exterior layer andan interior food contact layer. An oxygen barrier layer may be anethylene vinyl alcohol copolymer (EVOH) or PVDC. The gas barrier layersof the heat shrinkable food package are described above with referenceto the multilayer heat shrinkable packaging films.

One or more tie layers may also be included. The tie layers of the heatshrinkable food package are described above with reference to themultilayer heat shrinkable packaging films.

Preferably, the food package is a case-ready meat product comprising afresh meat product that includes myoglobin. Case-ready meat products canbe generally defined as fresh meat that is prepackaged and optionallyprelabeled at a centralized location and delivered to the retail marketprepared for final sale. Increasingly, meat products such as groundbeef, turkey and chicken products delivered to U.S. domesticsupermarkets for retail sale are delivered in case-ready packaging. Formany supermarkets, especially so-called “mega-grocery stores,”case-ready meat products provide not only cost savings in terms ofminimizing or eliminating on-site butchering and packaging, but alsoincreased sanitation and decreased incidence of product spoilage.

Product packaging that preserves the desirable color of meat, especiallyfresh meat, can promote the merchantability and appeal of the meatproduct for consumers. To meet the increasing demand for case-ready meatproducts, the case-ready meat products preferably provide a specifiedweight and/or volume packaging of common meat products, such as chickenbreast and ground beef. The case-ready meat product can include athermoplastic flexible film to maintain freshness, such as a film asdescribed herein. The meat product may be provided fresh, frozen,thawed, enhanced, processed or cooked, and the films advantageouslyprovide protection at various temperatures. Selection of films forpackaging food products can include consideration of such criteria asbarrier properties, cost, durability, puncture resistance, flex-crackresistance, food packaging law compliance e.g. United States Food & DrugAdministration (FDA) approval, machinability, optical properties such asgloss and haze, printability, sealability, shrinkability, shrink force,stiffness, and strength. Packaging that preserves desirable meatcoloration can promote the merchantability of meat products.

In another aspect, the packaged food product includes a fresh meatcontacting a thin plastic film comprising a myoglobin blooming agent ona food contact surface, stretched around a foam tray that supports theproduct. The film is preferably a multilayer film that is sufficientlynon-permeable to oxygen so that the color of the meat can be preservedin a desirable color (e.g. red) for more than about three days,preferably for 5, 7, 10, 15 or more days. Preferably, the meat productis packaged in vacuum containers such as heat shrinkable pouches orbags, which are vacuum sealed and prevent oxygen contact with the meatuntil the package is opened. The vacuum container includes a foodcontact surface including the myoglobin blooming agent.

In prior art case ready applications the meat product is sometimespackaged in a modified atmosphere package (“MAP”), wherein the meat ismaintained in a sealed pocket containing a headspace with an atmospherethat is different than ambient air. For example, a MAP can maintain redmeat in carbon dioxide, with very low oxygen content e.g. in a multipackwhere the master package is subsequently opened and the containedindividual packages in oxygen permeable films are exposed to theatmosphere thereby causing the meat to bloom red. Also, the preferredcolor of fresh meat can be promoted and maintained using a MAP withenriched oxygen content. Similarly a MAP with small concentrations ofcarbon monoxide (CO) can be used to cause and maintain a preferred redcolor of fresh meat. Methods of treating fresh meat with carbon monoxideprior to packaging have also been developed for case ready packagingapplications. The bright red CO-myoglobin complex is referred to ascarboxymyoglobin. The presence of carbon monoxide can also disfavorablyimpact sales of CO-containing meat products among consumers.

It is contemplated that the present invention may be used in combinationwith MAP. For example, in a tray package where the heat shrinkable filmcontacts a significant portion but not all of the food product'sviewable surface, a CO containing atmosphere can be used to cause adesirable color on the food surface areas that do not make directcontact with the packaging film. This embodiment may beneficially beused e.g. in certain types of tray overwrap packaging where the film maytypically be in contact with the top surface of the food but not in allplaces along the side or in tray or non-tray packages of irregularshaped items having gaps between adjacent meat surfaces e.g. such as maybe found in bone in products such as whole birds or shaped products suchas crown ribs for roasting.

In some embodiments, the heat-shrinkable food package can be a cook-inpackage, and optionally the food package need not comprise a heatsealable layer. “Cook-in” is the term used to indicate a film, casing orbag in which a foodstuff is pasteurized or cooked. This film or bag isused to hold together, protect and/or form the shape of the foodstuff bya food processor (manufacturer) during the cooking or pasteurizationprocess after which the film may be removed (sometimes termed“stripped”), or may be left on as a protective barrier during shipping,and optionally left on during retail sale.

Food packages formed from multilayer films of the invention having twoto fourteen or more layers are contemplated herein, where each layer isselected from the group consisting of: layers comprising an abuse orheat resistant polymeric composition, tie layers, oxygen barrier layers,moisture barrier layers, bulk layers and sealant layers. Preferably, theexterior surface layer comprises an abuse resistant and/or sealantlayer. Also preferably, the interior surface layer is a sealant layer.Multilayer films may be made by any of the commonly known processes andtechniques including for example coextrusion, coating lamination,lamination or combinations thereof in tubular or sheet form usingvarious orientation or biaxial stretching techniques such as tentering,differential roller speed machine direction stretch, or bubbletechniques such as trapped, double or triple bubble processes.

Preferably, the food packages are heat-shrunken, using heat shrinkablefilms having a total free shrink at 90° C. or less of at least about10-110% or higher including any increment of 5% therebetween. Forexample, various embodiments of the heat-shrunken packages may haveemployed films having a total free shrink measured at 90° C. or less ofabout 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%,75%, 80%, 85%, 90%, 95%, 100%, 105%, 110%, or greater.

Referring now to FIG. 5, a cross sectional schematic of a meatcontaining tray 10 is depicted. Tray 11 has a bottom 12 with integralside walls 12 a and 12 b supporting a retail cut of meat 13 such aspork. Shrink film 14 overwraps the tray 11 and provides a hermetic seal15 a and 15 b all along the continuous sidewall 12 a, 12 b. The film 14is shrunken into intimate contact with MBA containing food contactsurface 17 in contact with meat surface 18. Meat sidewalls 19 a, 19 bare not in contact with the food contact layer 17 but instead areexposed to a modified atmosphere 16 of a gas such as carbon monoxide.The tray has an inside surface 20 which may also be coated with an MBAto fix color on the meat bottom surface 21.

Referring now to FIG. 6 a top view of a package 20 depicts a myoglobincontaining food 21 such as a bone in cut of meat wrapped in a shrunkenshrink film 22 having a MBA coated food contact surface in contact withthe meat. The film is transparent to allow perception of the color andmeat surface characteristics.

Referring now to FIG. 7 a cross sectional schematic of a meat containingform shrink container 30 is depicted having a myoglobin containing cutof fresh meat 31 disposed in a thermoformed pocket 32 which is heatsealed to a heat shrinkable film 33 around the meat cut at heat seal 34a which is continuous and joins heat seal 34 b to form a hermetic vacuumpackage having a reduced oxygen atmosphere with intimate contact betweenthe MBA containing surfaces of film 32 and 33. The thermoformed pocket32 may be formed from any film suitable for thermoforming, including,for example, blown films, cast films, oriented films and non-orientedfilms. Typically, a film having less than 10% shrink (i.e., non-shrink)is employed for the forming film.

In the following examples, all layers are extruded or coextruded as aprimary tube, which is then biaxially oriented in a manner similar tothat broadly described in the aforementioned U.S. Pat. Nos. 3,456,044;5,759,648; 6,316,067; and 6,773,820; and published U.S. PatentApplication No. 2004/0166262; where the primary tube leaving the die isinflated by a trapped volume of air, which is cooled after exiting thedie with tap water and collapsed, and then oriented by reinflating toform a secondary tube termed a “bubble” by reheating to the film'sorientation (draw) temperature range for biaxial orientation. Thereheating can be accomplished by various means, for example, by radiantheaters or contact with hot air and/or water. Machine direction (MD)orientation is produced by pulling or drawing the film tube e.g. byutilizing multiple sets of nip rollers traveling at different speeds,and transverse direction (TD) orientation is obtained by radial bubbleexpansion. The oriented film is set by rapid cooling.

Biaxial orientation can be performed in any suitable manner, preferablyusing pressurized air to inflate the primary tube and mechanicallystretching the film while at or above the orientation temperature.Cooling of oriented films can be accomplished by means of a concentricair ring or by contact with any cooling medium.

Experimental results and reported properties are based on the followingtest methods or substantially similar test methods unless notedotherwise.

Oxygen Gas Transmission Rate (O₂ GTR): ASTM D-3985-81

Water Vapor Transmission Rate (WVTR): ASTM F 1249-90

Gauge: ASTM D-2103

Melt Index: ASTM D-1238, Condition E (190° C.) (except for propene-based(>50% C₃ content) polymers tested at Condition TL (230° C.))

Melting point: ASTM D-3418, DSC with 5° C./min heating rate

Gloss: ASTM D-2457, 45° angle

Shrinkage values are defined to be values obtained by measuringunrestrained shrink of a 10.0 cm square sample immersed in water at 90°C. (or the indicated temperature if different) for five seconds. Fourtest specimens are cut from a given sample of the film to be tested. Thespecimens are cut into squares of 10.0 cm length in the machinedirection (MD) by 10.0 cm length in the transverse direction (TD). Eachspecimen is completely immersed for 5 seconds in a 90° C. (or theindicated temperature if different) water bath. The specimen is thenremoved from the bath and the distance between the ends of the shrunkenspecimen is measured for both the machine direction (MD) and transversedirection (TD). The difference in the measured distance for the shrunkenspecimen and the original 10.0 cm side is multiplied by ten to obtainthe percent of shrinkage for the specimen in each direction. Theshrinkage of four specimens is averaged for the MD shrinkage value ofthe given film sample, and the shrinkage for the four specimens isaveraged for the TD shrinkage value. As used herein the term “heatshrinkable film” means a film having an unrestrained shrinkage value ofat least 10% in at least one direction at 90° C. The term “total freeshrink” refers to the sum of the shrink percentages in the MD and TDdirections.

The shrink force of a film is that force required to prevent shrinkageof the film and is determined from film samples taken from each film.Four film samples are cut 1″ (2.54 cm) wide by 7″ (17.8 cm) long in themachine direction and 1″ (2.54 cm) wide by 7″ (17.8 cm) long in thetraverse direction. The average thickness of the film samples isdetermined and recorded. Each film sample is then secured between thetwo clamps spaced 10 cm apart. One clamp is in a fixed position and theother is connected to a strain gauge transducer. The secured film sampleand clamps is then immersed in a silicone oil bath maintained at aconstant, elevated temperature for a period of five seconds. During thistime, the force in grams at the elevated temperature is recorded. At theend of this time, the film sample is removed from the bath and allowedto cool to room temperature whereupon the force in grams at roomtemperature is also recorded. The shrink force for the film sample isthen determined from the following equation wherein the results areobtained in grams force per mil of film thickness (g/mil). Shrink Force(g_(F)/mil)=F/T wherein F is the force in grams and T is the averagethickness of the film samples in mils.

Shrinkage values, shrink force, and free shrink are measured by themethods described above or tests similar thereto, unless otherwisespecified. Other useful tests are provided by the following references,which are incorporated herein in their entirety: U.S. Pat. Nos.6,869,686; 6,777,046 and 5,759,648.

Provided below are non-limiting examples of the compositions, films andpackages disclosed herein. In all the following examples, unlessotherwise indicated, the film compositions are produced generallyutilizing the apparatus and method described in U.S. Pat. No. 3,456,044(Pehlke), which describes a coextrusion type of double-bubble method,and in further accordance with the detailed description above. Allpercentages are by weight unless indicated otherwise.

Multilayer tubular films are made by a biaxial stretching orientationprocess. Films of 3, 4, 5, 6, 7, 8, 9 or more layers are contemplated.The inventive multilayer films may include additional layers or polymersto add or modify various properties of the desired film such as heatsealability, interlayer adhesion, food surface adhesion, shrinkability,shrink force, wrinkle resistance, puncture resistance, printability,toughness, gas or water barrier properties, abrasion resistance andoptical properties such as gloss, haze, freedom from lines, streaks orgels. These layers may be formed by any suitable method includingcoextrusion, extrusion coating and lamination.

Examples 1-2

A monolayer and a two layer coextruded heat shrinkable oxygen barrierfilm are provided. The film compositions of Examples 1-2 are producedunder similar conditions. For each example listed in Table 1 thecomponents are blended in the indicated weight ratio followed by heatplastification and extrusion of a tube as generally described above.Draw point temperature and bubble cooling rates are adjusted to maximizebubble stability, and expected properties of each film are reported inTable 1. The films are extruded in the form of a seamless tube. Thetubes are wound on reels and the end of each tube is secured by tape.Examples 1 and 2 represent identical films except that in the film ofExample 2 the reeled tube is then annealed in a circulating hot air ovenat about 38° C. to dimensionally stabilize the tube. During annealing,the tube flat width is reduced by shrinkage.

The expected properties of an unannealed and annealed film of acontemplated embodiment of the present invention are reported inExamples 1 and 2 respectively. The amorphous nylon copolymer andcopolyamide blend of Examples 1 and 2 may form a shrinkable film whichis easy to orient with good optical properties including very highgloss. The copolyamide is a commercially available nylon 6/12 (GrilonCR9) and the blend may include added anti-oxidant and antiblock. Theunannealed film of example 1 is expected to have very high freeshrinkage relative to annealed Example 2. Annealing reduces theshrinkage.

A comparison of the expected haze, gloss and tensile strength propertiesof the unannealed film of Example 1 with the annealed film of Example 2indicates that annealing may modify or improve some properties relativeto unannealed film.

Both the annealed and unannealed casings are slugged with a concentratedaqueous solution of sodium nitrite and allowed to dry to produce acoating of myoglobin blooming agent on the interior casing surface in anamount of from about 0.05 to 10 μmoles/in².

An annealed sodium nitrite coated tube according to Example 2 of thepresent invention may be used as a ground beef, ground pork or sausagecasing. This transparent tube may be stuffed with a beef and/or porkemulsion, and may be subsequently cooked. The resultant sausage casingis expected to promote and maintain a desirable red color prior tocooking and provide oxygen barrier properties having an oxygentransmission rate of less than 310 cm³/m²/24 hours measured at 0%relative humidity and 23° C. The desired color is expected to bemaintained for at least 5 days and preferably at least 15, 25, 30 ormore days after stuffing and color fixing/blooming and before cooking.Optionally, the encased product may be cooked and is expected to have agood yield with uniform adhesion of the casing to the stuffed meat.

TABLE 1 Tensile Strength × A:B 10³ Shrink % Nylon Blend Wt. (psi) at 90°C. # A B Ratio Gloss MD/TD MD/TD 1+ 6/12 amorphous 4:1 90 23/23 51/49nylon copolymer* 2++ 6/12 amorphous 4:1 98 20/24 14/9  nylon copolymer**A nylon 6I/6T copolymer sold under the brand name Selar PA 3426+Unannealed film ++Annealed film

Examples 3-9

Biaxially stretched two layer oxygen barrier films having three and fourcomponent nylon blends in one layer coextruded with a secondpolyethylene heat sealable food contact layer may be made according tothe present invention as demonstrated by the compositions and propertiesof the films described in Examples 3-9. Blends of an amorphous nyloncopolymer such as nylon 6I/6T and a crystalline copolyamide having amelting point above 145° C. such as a commercially available nylon 6/12(Grilon CR9) or nylon 6/69 may be made with one or more other nylon 6/12copolymers, nylon 6/66 copolymers or nylon homopolymers such as nylon 6,nylon 11, and nylon 12.

Each two layer film is extruded and biaxially stretched (oriented) by aknown double bubble extrusion process (See e.g. U.S. Pat. No.3,456,044). In forming the primary film tube, the nylon resins areconventionally blended. The nylon blend and a polyethylene such as VLDPEare each heat plastified in separate conventional single screw extrudersequipped with a standard commercially available polyethylene screw andthe melts are brought together in a conventional die having a diediameter of about 1.25 inches. The extruder barrel temperature may rangefrom 175° C. to about 235° C. and the die temperature may be set atabout 224° C. The machine direction (MD) orientation ratio may be fromabout 2 to 2.5 and the transverse direction (TD) orientation ratio maybe from about 2 to 3.

Two layer films having various nylon blend components are listed inTable 2 as Examples 3-9. In all of these examples the blends areexpected to produce bioriented films having good shrink properties inboth the machine direction and the transverse direction with shrinkagevalues similar to those indicated in Table 2.

The optional addition of nylon homopolymers may improve gas barrierproperties by lowering permeability. In examples 7 and 9, the nylon 6and nylon 12 polymers, are commercially available nylon homopolymerse.g. such as those sold under the respective brand names Grilon F40(nylon 6) and Grilamid L25 (nylon 12) by Ems-Chemie (North America) Inc.of Sumter, S.C., USA. In example 8, the nylon 11 polymer may be acommercially available nylon homopolymer e.g. such as that previouslyavailable under the trade name Rilsan nylon 11 from Rilsan Corporationof Glen Rock, N.J. O₂TR values are expected to be less than theindicated values.

The films of Examples 3-9 may be sprayed on the polyethylene layer witha starch containing a myoglobin blooming agent e.g. as a blend of sodiumnitrite, sodium nitrate, starch, and anti-oxidant before or after beingfabricated into heat shrinkable bags and pouches by heat sealing thepolyethylene layer to itself. The bags may be used to vacuum packagebeef, pork and poultry. The films coated with the myoglobin bloomingagent may be used to vacuum package fresh meat on a polymeric oxygenbarrier tray or in form shrink applications. Packages of meat so madeare expected to develop and maintain a desirable color for at least 5,and preferably 10 and more preferably 15 or more days after packaging.The penetration of a pink or red color into the meat is desirablycontrolled to remain within about ¼ inch or less from the meat surfaceby adjusting the amount of agent on the surface to an appropriate valuebelieved to be between about 0.05 to 10 μmoles/in².

TABLE 2 Nylon Blend Components Nylon O₂TR Amorphous 6/12** Nylon SHRINK% cm³/m² Nylon* mp >145° C. 6/12*** at 90° C. 24 hr/ # wt. % wt. % wt. %Other Nylon wt. % M.D./T.D. 1 atm 3 10 72 18 30/20 <100 4 20 72 8 40/40<100 5 18 57.6 14.4 nylon 6/66+ 10 30/20 <50 6 18 57.6 14.4 nylon 6/12++10 40/40 <50 7 18 57.6 14.4 nylon 6+++ 10 30/20 <50 8 18 57.6 14.4 nylon11++++ 10 30/30 <50 9 18 57.6 14.4 nylon 12+++++ 10 30/30 <50 *Amorphousnylon 6I/6T copolymer - Selar PA 3426 (trademark of DuPont). **A nyloncopolyamide of nylon 6/12 - Grilon CR9 (trademark of Ems-Chemie). ***Anylon copolyamide of nylon 6/12 - Grilon CA 6E (trademark ofEms-Chemie). +Ultramid C33 (trademark of BASF). ++Zytel 151 (trademarkof DuPont). +++Grilon F40 (trademark of Ems-Chemie). ++++Rilsan(trademark of Arkema division of Total). +++++Grilamid L25 (trademark ofEms-Chemie).

Example 10

A 40 by weight % solids sodium nitrite solution may be prepared bydissolving 8 kg of NaNO₂ in 12 kg of water. The solution is made withtap water at room temperature by gently agitating the water/nitritemixture.

A polyethylene such as Dow ATTANE® 4201-G VLDPE (commercially availablefrom Dow Chemical Company, Midland, Mich.) is loaded into the hopper ofa gravimetric dosing unit that is positioned to feed the polymer intothe main feed port of a twin screw extruder. The feeder is configured todose the polyethylene at a rate of about 40 kg/h. The mixing elements ofthe twin screw extruder are arranged in a fashion that allow for feedingand melting of the VLDPE, injection and mixing of the water/nitritesolution, removal of the water, pressurization of a die and formation ofcontinuous strands of a homogeneous and uniform polyethylene/nitriteblend.

The twin screw extruder is heated to about 200-330° F. and the extruderscrews rotated with polyethylene introduced into a primary feed port ata rate of about 40 kg/hour with the nitrite/water mixture being injectedinto the molten polymer at a delivery rate of about 5 to 6 kg/h rate ina manner sufficient to deliver a nitrite concentration in polymer afterwater removal of about 5% by weight.

Mixing elements of the extruder may be arranged in a fashion to preventthe liquid water/nitrite solution from moving upstream to the primaryfeed port. For example, full bore orifice plugs may be used to preventunwanted upstream migration.

Following injection, the water fraction of the nitrite/water solutionmay evaporate through a vent port. After mixing, the blend is extrudedthrough a die, cooled in a water bath and pelletized and dried.

Examples 11-19

In examples 11-19, multilayer heat-shrinkable food packaging films areprepared from masterbatch pellets made in a manner similar to thatdescribed above in Example 10. The loading level of 5% sodium nitritemasterbatch pellets is varied to produce VLDPE films with differentloadings of sodium nitrite. The sodium nitrite myoglobin blooming agentis included in the sealant layer of each film, which also forms theinterior, food-contact layer of each multilayer film. Three, six andseven-layer films with a sealant layer comprising a myoglobin bloomingagent in the sealant food-contact layer are prepared. Table 3 summarizesthe configuration and composition of certain preferred heat-shrinkablemultilayer films. The column designated “% MBA” provides the percentageof myoglobin blooming agent in the sealant layer. Columns designated“N/A” mean the indicated structural layer was omitted (except inExamples 13 and 14 where the core layer/has the same formulation as theouter layer and the total of both layers is presented in the outer layercolumn). The basis weight and the percent thickness of each layer withrespect to the multilayer film are also shown in Table 3. In eachexample of Table 3 PANS represents one or more processing aids and/orslip agents. Also, in each example the oxygen barrier layer denoted inTable 3 as PVDC comprises a 5.5:1 blend of vinylidenechloride-methylacrylate copolymer and vinylidene chloride-vinyl chloridecopolymer and a minor amount (about 2-3%) of conventional plasticizing,lubricating and/or coloring additives such as ultramarine blue, e.g. asdescribed in U.S. Pat. No. 4,798,751 which is hereby incorporated byreference in its entirety. While PVDC oxygen barrier layers areexemplified in Table 3, EVOH oxygen barrier layers can also be used orpolyamides such as MXD6 or 6I/6T and blends of nylons and/or EVOH arecontemplated.

The polymers represented in the examples are identified as followsunless otherwise noted.

EVA1 is a copolymer of ethylene and vinyl acetate (EVA) available fromExxonMobil Chemical Company of Houston, Tex., U.S.A. under the trademarkEscoreneJ LD 701.ID. It reportedly has the following properties: 10.5wt. % vinyl acetate content, 0.93 g/cm³ density, 0.19 dg/min. meltindex, and a melting point (mp) of about 97EC.

EMA1 comprises an ethylene methyl acrylate copolymer which is a strongadhesive polymer. It has a reported density of about 0.948 g/cm³, a meltindex of 2.0 dg/min. and a melting point of 93EC and a softening pointof 49EC and is available under the trademark Emac+ SP 1330 from theVoridian division of Eastman Chemical Company, of Kingsport, Tenn.,U.S.A.

EAO1 comprises a copolymer predominantly of ethylene with butene-1monomer. It has a reported density of about 0.888 g/cm³, a melt index of2.2 dg/min., a melting point of 70EC and is available under thetrademark Exacts 4053 from ExxonMobil Chemical Company of Houston, Tex.,U.S.A.

EAO2 is an ethylene α-olefin copolymer having a reported density ofabout 0.895 g/cm³, a melt index of 1.0 dg/min., a melting point of about90EC and is available under the trademark Exacts 9523 from ExxonMobilChemical Company.

EAO3 comprises an ethylene-α-olefin copolymer of very low densitypolyethylene sold by Dow Chemical Company of Midland, Mich., U.S.A.under the trademark ATTANEJ XU 61509.32. It is a copolymer of ethyleneand octene-1 reportedly having: a melt index of about 0.5 dg/min.; adensity of about 0.912 g/cm³; and a dominant melting point of about122-123EC with a second significant peak at about 105EC and a minor peakat about 119EC.

EAO4 comprises an ethylene-α-olefin copolymer of very low densitypolyethylene sold by Dow Chemical Company of Midland, Mich., U.S.A.under the trademark ATTANEJ XU 61520.16. It is a copolymer of ethyleneand octene-1 with antioxidant reportedly having: a melt index of about0.5 dg/min.; a density of about 0.912 g/cm³; a Vicat softening point of95EC; and a dominant melting point of about 122-123EC, a secondsignificant peak at about 104EC, and a minor peak at about 119EC.

The exterior layer of Examples 11 and 12 comprised a blend AA of 40 wt.% EVA1: 30 wt. % EAO1: 23.5% EAO3: 6.5% PA/S. In Table 3, the followingblend designations apply. Blend BB is a combination of 18% EVA1: 60%EAO2: 19% EAO3: 3% PA/S. Blend CC is a combination of 18% EVA1: 60%EAO2: 15% EAO3: 7% PA/S. Blend DD is a combination of 22% EVA1: 45%EAO2: 28% EAO3: 5% PA/S. Blend EE is a combination of 27% EVA1: 45%EAO2: 25% EAO3: 3% PA/S. Blend FF is a combination of 27% EVA1: 45%EAO2: 25% EAO4: 3% PA/S. Blend GG is a combination of 49% EAO1: 45%EAO3: 6% PA/S.

TABLE 3 Multilayer Food Packaging Films Containing Myoglobin BloomingAgent (MBA) Oxygen Outer Layer Core Layer 1 Tie Layer 1 Barrier LayerTie Layer 2 Core Layer 2 Sealant Layer Ex. No. % [Basis (% [Basis (%[Basis (% [Basis (% [Basis (% [Basis (% [Basis (% No. Layers MBAThickness)] Thickness)] Thickness)] Thickness)] Thickness)] Thickness)]Thickness)] 11 3 0.80% AA N/A N/A PVDC N/A N/A 16% MB(5%) 37% EVA1 30%EAO1 10% PA/S [7.56 (25.1)] [5.33 (17.7)] [17.23 (57.2)] 12 3 1.25% AAN/A N/A PVDC N/A N/A 25% MB(5%) 35% EVA1 30% EAO1 10% PA/S [7.56 (25.1)][5.33 (17.7)] [17.23 (57.2)] 13 6 1.75% BB N/A 100% EMA1 PVDC 100% EMA1GG 35% MB(5%) 14% VLDPE1 45% EAO1 6% PA/S [9.13 (30.4)] [1.50 (5.0)][4.96 (16.5)] [1.50 (5.0)] [9.16 (30.5)] [9.16 (30.5)] 14 6 1.25% BB N/A100% EMA1 PVDC 100% EMA1 GG 25% MB(5%) 37% EVA1 30% EAO1 8% PA/S [8.83(29.3)] [2.40 (8.0)] [5.33 (17.7)] [2.40 (8.0)] [8.60 (28.6)] [2.56(8.5)] 15 7 1.75 CC EE 100% EMA1 PVDC 100% EMA1 100% EAO3 35% MB(5%) 27%EVA1 30% EAO1 8% PA/S [5.93 (19.2)] [5.93 (19.2)] [2.40 (7.8)] [5.33(17.3)] [2.40 (7.8)] [6.99 (22.7)] [1.83 (5.9)] 16 7 1.25 BB BB 100%EMA1 PVDC 100% EMA1 GG 25% MB(5%) 24% VLDPE1 45% EAO2 6% PA/S [4.21(14.0)] [4.21 (14.0)]  [1.5 (5.0)] [4.96 (16.5)]  [1.5 (5.0)] [9.16(30.5)] [4.51 (15.0)] 17 7 1.25 DD 100% EAO4 100% EMA1 PVDC 100% EMA1100% EAO4 25% MB(5%) 43.5% VLDPE2 22% EVA1 9.5% PA/S [7.26 (18.8)] [7.26(18.8)] [2.57 (6.7)] [6.35 (16.5)] [2.57 (6.7)] [9.95 (25.8)] [2.56(6.6)] 18 7 1.25 CC FF 100% EMA1 PVDC 100% EMA1 100% EAO4 25% MB(5%) 45%EAO2 18% VLDPE2 12% PA/S [7.26 (18.8)] [7.26 (18.8)] [2.57 (6.7)] [6.35(16.5)] [2.57 (6.7)] [9.95 (25.8)] [2.56 (6.6)] 19 7 1.75 CC FF 100%EMA1 PVDC 100% EMA1 100% 35% MB(5%) VLDPE2 45% EAO2 8% VLDPE2 12% PA/S[7.26 (18.8)] [7.26 (18.8)] [2.57 (6.7)] [6.35 (16.5)] [2.57 (6.7)][10.68 (27.7)]  [1.83 (4.8)] % MBA = percentage of myoglobin bloomingagent in food contact layer Basis = weight basis in pounds per 3000square feet; % Wt = weight percent of multilayer film MB(5%) is amasterbatch as defined in Example 10 N/A = layer is not present instructure

In Examples 11-19, one extruder is used for each layer and the heatplastified resins from each extruder are introduced to a 3-layer die forexamples 11 and 12, and a 7-layer spiral plate coextrusion die forexamples 13-19. To make a six-layer film from a seven layer spiral platecoextrusion die, the resin or resin mixture to form an individual layercan be extruded through more than one die positions to produce one layerfrom two or more die locations. For example, the outer layer of films 13and 14 is made by coextruding the component materials from two portions(i.e. outer layer and core layer 1) of the seven layer die to form onecontinuous outer layer in the film. The weight ratios of each layer aregiven in Table 3 as the basis weight. The thickness of the film layer asa percentage of the total film thickness is also provided in Table 3.

For each layer, the resin or resin mixture is fed from a hopper into anattached single screw extruder where the resin and/or mixture is heatplastified and extruded through a die into a primary tube and cooled.The extruded multilayer primary tube is cooled by spraying with cold tapwater (about 40°-60° F.).

The cooled primary tube is flattened by passage through a pair of niprollers whose speed is controlled to neck down the primary tube toadjust the tube circumference or flatwidth. A flattened tube of about2-12 inches or more flatwidth is preferred. The cooled flattened primarytube is reheated, biaxially stretched, and cooled. The cooled film isflattened, and the biaxially stretched and biaxially oriented film iswound on a reel. The machine direction (MD) draw or orientation ratio isabout 4:1 to 5:1 and the transverse direction (TD) bubble or orientationratio is about 3:1 to 4:1. The draw point or orientation temperature isbelow the predominant melting point for each layer oriented and abovethat layer's glass transition point. Draw point temperature, bubbleheating and cooling rates and orientation ratios are generally adjustedto maximize bubble stability and throughput for the desired amount ofstretching or orientation. Exemplary values expected for the free shrinkand other properties such as gauge thickness, gloss, and oxygentransmission rate of the films described in Table 3 are given in Table 4below. The films 11-19 are preferably made with a thickness of betweenabout 1.5 and 2.5 mils. The ratio of the basis weights in Table 3 can beproportionally varied to provide films having different totalthicknesses e.g. from about 1.0 to 5.0 mils, with comparable relativethicknesses between layers. Films may be made with any suitablethickness with suitably sized equipment and appropriate parameterselection which may be determined by those skilled in the art withoutundue experimentation. The films are transparent and expected to havegood optical properties including haze values which may be 35 to 15% orless. The shrink force values are expected to be typical for films madeby the double bubble process and in the range of e.g. of about 35 to 75Kg/cm in each of the MD and TD at 90° C., and in the range of about 15to 55 Kg/cm for residual shrink force at room temperature (˜20-23° C.)Higher and lower values as desired may be obtained by altering processparameters and/or film formulations without undue experimentation.Shrinkage values at lower temperatures are expected to provide at least10% shrink in at least one of the MD and TD and preferably both the MDand TD at lower temperatures such as 80° C. and 74° C. Exemplary valuesof expected film properties may also be seen in U.S. Pat. Nos.6,815,023; 6,773,820; 6,316,067; and 5,759,648. Exemplary values ofcertain expected properties are reported in Table 4 below.

TABLE 4 O₂TR cm³/m²/ 24 hrs/ Gauge MD TD Total % at 1 atm, Ex. milShrink Shrink Free 0% RH & Gloss No. (μ) (90° C.) % (90° C.) % Shrink23° C. at 45° 11  2 55 60 115 0.9-1.5 65-75 (50) 12  2 55 60 115 0.9-1.565-75 (50) 13  2 54 60 114 0.9-1.5 65-75 (50) 14  2 55 60 115 0.9-1.565-75 (50) 15  2 55 60 115 0.9-1.5 65-75 (50) 16  2 55 60 115 0.9-1.565-75 (50) 17   2.5 48 55 103 0.9-1.5 65-75 (63) 18   2.5 48 55 1030.9-1.5 65-75 (63) 19   2.5 48 55 103 0.9-1.5 65-75 (63)

While the values for shrink at 90° C. in Table 4 are typical targetvalues based on repeated trials, the free shrink can vary between trials

Meat such as fresh poultry or pork inserted into pouches and bags madefrom the above films followed by evacuation of the atmosphere within thebag and sealing to provide a hermetic seal and shrinking by briefexposure to elevated temperatures to effect the same will result in atransfer of the MBA to the meat surface and within about 3 days or lesspromote, cause and/or fix a desired color bloom which may last manyweeks when the oxygen barrier vacuum package is stored underrefrigeration, conditions. The same effect may be obtained in othermyoglobin containing products however it is expected that for productshaving a high concentration of myoglobin such as beef a much higheramount of MBA may be need to achieve the desired effect. Due to thecompeting action of other moieties for attachment to the heme siteinsufficient MBA may not only not produce the desired color change butan undesirable purple or brown may be apparent in the absence ofsufficient MBA. For poultry or pork it is expected that amounts of MBAin the range of 0.01 to 2 (a preferred range e.g. for typical cuts ofpork is from at least 0.05 to 1.25) μmole/inch² of the myoglobinblooming agent on a food contact surface may be sufficient to producethe desired color e.g. a reddish hue, while for beef higherconcentrations above 2 are desired.

For beef it is expected that amounts of at least 5% or more of an MBAsuch as sodium nitrite may be needed in the food contact layer.

In some embodiments, the film, bag, process and package provided hereincomprise heat sealable, oxygen and moisture barrier films for holding afoodstuff during cooking and/or for packaging for sale of such afoodstuff after a pasteurization or cooking period.

In another embodiment of the invention, A food package may comprise amyoglobin-containing food product such as fresh meat having a watercontent of at least 5 wt. %; and a container comprising a heatshrinkable, oxygen barrier thermoplastic film having a polymeric foodcontact layer and a tray; wherein the container encloses the foodproduct in a reduced oxygen environment; and the food product ismaintained in a modified atmosphere comprising a nitrogen or sulfurcontaining gaseous myoglobin blooming agent, or mixtures thereof. TheMBAs described throughout this specification may also be used in thisembodiment. It is further contemplated that either gaseous ornon-gaseous MBAs may be used as well as combinations thereof in variousembodiments of the invention.

It should be appreciated that films and packages made according to thepresent invention may be made and employed which are free frommarinades, flavorants, food grade water soluble adhesives, starches,spices, sodium chloride, animal or vegetable oils and the like and othercompounds described herein as optional ingredients which may be coatedor otherwise present on an exterior or interior packaging film surface.

Examples 20-33

Examples 20-33 describe various methods that may be used to produce afilm contact surface having MBA thereon. Examples 20 to 24 describevarious methods that may be used to prepare a masterbatch containing anMBA for subsequent use in making various film embodiments according tothe present invention. Additional information on these methods aredisclosed in a U.S. patent application to Nelson, et al. entitled,“Process for Introducing an Additive into a Polymer Melt” filed Apr. 20,2006 which application is hereby incorporated by reference in itsentirety. Examples 25 to 33 describe methods for surface application byvarious means.

Example 20

Sodium nitrite powder (Rapauno Products NaNO₂ obtained from HydriteChemical Company, Brookfield, Wis.) and Dow ATTANE® 4201-G VLDPE(obtained from Dow Chemical Company, Midland, Mich.) are combined toform a masterbatch with a corotating twin screw extruder. The extruderis heated to 330° F. and the sodium nitrite and VLDPE are simultaneouslyadded to the primary feed port. Selections of the sodium nitrite andVLDPE addition rates are made such that the composition of the mixtureis 95% VLDPE and 5% sodium nitrite by weight. The twin screw extruder isconfigured to disperse the sodium nitrite powder such that theindividual powder particles are surrounded by polymer. The discharge ofthe extruder is fitted with a die of geometry appropriate for shapingthe sodium nitrite-VLDPE mixture into continuous strands. The strandsare cooled in a water bath. At the exit of the water bath, an air kniferemoves some of the moisture clinging to the surface of the stands.After leaving the influence of the air knife, the strands are cut intodiscrete pellets by a rotating knife-style pelletizer. Those pellets aredried in a convection oven at about 50° C., packed in aluminum foilcontaining bags and stored for use.

Example 21

Repauno Products NaNO₂ is passed through a rotary pulverizer (e.g.,Wiley Mill obtained from Brabender GmbH and Company, Duisburg, Germany).The rotary pulverizer reduces the average particle size of the sodiumnitrite powder. The pulverized sodium nitrite is combined with DowATTANE® 4201-G VLDPE in the same proportions using the same techniquedescribed in Example 20 to form a masterbatch.

Example 22

A 40% solids sodium nitrite solution is prepared by dissolving 8 kg ofRepauno Products NaNO₂ in 12 kg of water. The solution is made with tapwater at room temperature by gently agitating the water/nitrite mixture.

The nitrite solution is spray dried (e.g., Mobile Minor spray dryer fromNiro, Inc. Columbia, Md.) to form a homogeneous powder. The spray driedsodium nitrite is combined with Dow ATTANE® 4201-G VLDPE in the sameproportions using the same technique described in Example 20 to form amasterbatch.

Example 23

A 40% solids sodium nitrite solution is prepared in a manner describedin Example 22.

Dow ATTANE® 4201-G VLDPE is loaded into the hopper of a gravimetricdosing unit that is positioned to feed the polymer into the main feedport of a corotating twin screw extruder. The extruder is heated to 330°F. and the VLDPE is continuously metered into the extruder where itmelts. The 40% solids nitrite/water solution is injected into the moltenVLDPE with a gear pump at a rate such that the concentration of thesolution is 11.6% by weight. The water portion of the solution vaporizesin the extruder and is removed via a vent port. The remainder of thecomposition is substantially a mixture of VLDPE and sodium nitrite witha sodium nitrite content of 5% by weight. The resultant mixture isshaped into strands with a die, cooled with water, blown dry with air,chopped into pellets, dried and packaged as described in Example 20.

Example 24

A 4% solids sodium nitrite solution is prepared by dissolving 0.25 kg ofRepauno Products NaNO₂ in 6 kg of methanol (from Hydrite ChemicalCompany, Brookfield, Wis.).

The sodium nitrite/methanol solution is combined with Dow ATTANE® 4201-GVLDPE in the same proportions using the same technique described inExample 23 to form a masterbatch. The resultant blend is 0.5% by weightof sodium nitrite.

Examples 25

Spray-dried sodium nitrite is prepared with the materials and methoddescribed in Example 22. The powder is applied in a uniform layer usingan electrostatic sprayer (e.g., obtainable from Oxy-Dry Corporation,Itasca, Ill.) to the food contact surface of a shrink film. The film isfabricated into a shrink bag.

Example 26

A 40% solids sodium nitrite solution is prepared in a manner describedin Example 22.

A continuous shrink film tubing is passed between two sets of niprollers, one set located above the other. The nips are separated bysufficient space such that the tubing is able to inflate with injectedair and exhibit a circular cross section without wrinkling. The inflatedtubing is momentarily slit and the air cavity is “slugged” (i.e.,replaced) by the 40% solids sodium nitrite solution. The slitting deviceis removed and the inner surface of the tubing is coated with the sodiumnitrite solution.

Example 27

A 40% solids sodium nitrite solution is prepared in a manner describedin Example 22.

The food contact surface of a shrink film is coated with a 40% solidssolution of sodium nitrite. The solution is applied to the food contactsurface and is metered with a #8 wire wound rod (e.g., Mayer rod orequalizer). Following coating, the water is removed using a heated,forced air oven.

Example 28

A 40% solids sodium nitrite solution is prepared in a manner describedin Example 22.

The food contact surface of a shrink film is coated with a 40% solidssolution of sodium nitrite. The technique is the same as described inExample 27 except that the metering method uses a smooth rod.

Example 29

A 40% solids sodium nitrite solution is prepared in a manner describedin Example 22.

The food contact surface of a shrink film is coated with a 40% solidssolution of sodium nitrite. The technique is the same as described inExample 27 except that the metering method uses a gravure applicator.

Example 30

A 40% solids sodium nitrite solution is prepared in a manner describedin Example 22.

The food contact surface of a shrink film is coated with a 40% solidssolution of sodium nitrite. The technique is the same as described inExample 27 except that the metering method uses a flexographic printingplate.

Example 31

A 40% solids sodium nitrite solution is prepared in a manner describedin Example 22.

The food contact surface of a shrink film is coated with a 40% solidssolution of sodium nitrite. The technique is the same as described inExample 27 except that the metering method uses transfer rolls.

Example 32

A 40% solids sodium nitrite solution is prepared in a manner describedin Example 22.

The food contact surface of a shrink film is coated with a 40% solidssolution of sodium nitrite. The technique is the same as described inExample 27 except that the metering method uses a spray applicator.

Example 33

A 40% solids sodium nitrite solution is prepared in a manner describedin Example 22.

A coating composition is prepared by combining 5 g of a polyethyleneoxide polymer, 5 g of distilled water and 0.3 g of the 40% solids sodiumnitrite solution. The food contact surface of a shrink film is coatedwith the coating composition using the technique described in Example27.

The shrink films made according to the above methods are all believed tobe suitable to package a myoglobin containing food product and fix adesired color e.g. red within 72 hours after packaging under a reducedoxygen e.g. vacuum packaging operation. The intimate contact between thefood contact layer having the MBA and the meat surface effects atransfer to the meat producing the desired color, which is expected tolast for many weeks.

the MBA coated shrink films according to the present invention may alsobe used in form shrink applications such as those made using Multivac R550, R250 and R 150 thermoforming machines

Films, bags and packages may also employ combinations of characteristicsas described in one or more embodiments and selected therefrom.

The above examples are illustrative only, and should not be interpretedas limiting since further modifications of the disclosed embodimentswill be apparent to those skilled in the art in view of this teaching.All such modifications are deemed to be within the scope of theinvention disclosed herein.

1. A heat-shrinkable food packaging film having an interior surface andan exterior surface, the film comprising: (a) a food contact layercomprising a myoglobin blooming agent, and (b) an oxygen barrier layer;wherein the film has a free shrink value at 90° C. or less of at least10% in at least one direction; wherein the myoglobin blooming agent ispresent on the food contact layer surface in a concentration sufficientto produce a desirable surface coloration of the meat product andprevent undesirable extension of the color into the body of the meatproduct; wherein the concentration of myoglobin blooming agent isbetween 0.001 to 0.900 mg/in².
 2. A film, as defined in claim 1, whereinthe film has a total free shrink value at 90° C. or less of at least60%.
 3. A film, as defined in claim 1, wherein the oxygen barrier layercomprises PVDC, EVOH, polyamide, nanocomposite, PET, or a combinationthereof.
 4. A film, as defined in claim 1, wherein the film has anoxygen transmission rate of less than 310 cm³/m²/24 hours measured at 0%relative humidity and 23° C.
 5. A film, as defined in claim 1, whereinthe film has an oxygen transmission rate of less than about 75 cm³/m²/24hours measured at 0% relative humidity and 23° C.
 6. A film, as definedin claim 1, wherein the film has an oxygen transmission rate of lessthan 20.0 cm³/m²/24 hours measured at 0% relative humidity and 23° C. 7.A film, as defined in claim 1, wherein the film further comprises anexterior surface layer (c), and wherein the oxygen barrier layer (b) ispositioned between layer (a) and layer (c).
 8. A film, as defined inclaim 7, wherein the film is at least five polymeric layers and has afirst tie layer (d) positioned between the food contact layer (a) andoxygen barrier layer (b) and a second tie layer (e) positioned betweenthe oxygen barrier layer (b) and the exterior surface layer (c).
 9. Afilm, as defined in claim 7, wherein the exterior surface layer (c)comprises a homopolymer or a copolymer of nylon, polyethyleneterephthalate, polyolefin, or blends thereof.
 10. A film, as defined inclaim 1, wherein the food contact layer (a) comprises a homopolymer or acopolymer of a polyolefin or blends thereof.
 11. A film, as defined inclaim 7, wherein at least one layer of the film is crosslinked.
 12. Afilm, as defined in claim 7, wherein at least one layer of the film isirradiatively crosslinked.
 13. A film, as defined in claim 1, furthercomprising at least one additional layer of a polyamide, a polyester, apolyethylene, a polypropylene, a polybutylene, a polystyrene, apolyurethane, a polyacrylamide, an anhydride-modified polymer, anacrylate-modified polymer, or copolymers or blends thereof.
 14. A film,as defined in claim 1, wherein the myoglobin blooming agent is selectedfrom the group consisting of: Fremy's salt, nitrate salts having theformula (MNO₃) and inorganic nitrites (MNO₂), where the counter ion (M+)is selected from the group consisting of: alkali metals, alkaline earthmetals, transition metals, protonated primary, secondary or tertiaryamines, quaternary amines, and ammonium.
 15. A film, as defined in claim1, wherein the myoglobin blooming agent containing layer furthercomprises at least one of an antioxidant, a slip agent, an antiblockagent, a colorant, a flavorant, an odorant, an organoleptic agent, acoefficient of friction modifying agent, a lubricant, a surfactant, anencapsulating agent, an oxygen scavenger, a pH modifying agent, a filmforming agent, an emulsifier, a polyphosphate, a humectant, a dryingagent, an antimicrobial agent, a chelating agent, a binder, a starch, apolysaccharide or a combination thereof.
 16. A film, as defined in claim1, wherein the food contact layer comprises between about 0.10 weight %and about 5.0 weight % of the myoglobin blooming agent.
 17. A film, asdefined in claim 1, wherein the food contact layer comprises at leastabout 0.10 weight % and less than 2.0 weight % of the myoglobin bloomingagent.
 18. A film, as defined in claim 1, wherein the food contact layerhas on its food contact surface of from 0.01 to 10 μmole/inch² of themyoglobin blooming agent.
 19. A film, as defined in claim 1, wherein thefood contact layer has on its food contact surface of from 0.01 to 2μmole/inch² of the myoglobin blooming agent.
 20. A film, as defined inclaim 1, wherein the food contact layer has at least 0.1 mg/inch² of themyoglobin blooming agent.
 21. A film, as defined in claim 1, wherein thefood contact layer has an its food contact surface less than 0.25mg/inch² of the myoglobin blooming agent.
 22. A film, as defined inclaim 1, wherein the food contact layer comprises a heat sealablepolymer.
 23. A film, as defined in claim 1, wherein the food contactlayer comprises a heat sealable polymer selected from the group ofpolyolefin, polyethylene, VLDPE, LLDPE, LDPE, HDPE, ethylenealpha-olefin copolymers, polypropylene, polybutylene, and ionomer.
 24. Afilm, as defined in claim 1, wherein at least 10% of the surface area ofthe film is transparent.
 25. A film, as defined in claim 1, wherein thefilm has a gloss value of at least 70 at 45°.
 26. A food packagecomprising: a myoglobin-containing food product having a water contentof at least 5 wt. %; and a container comprising a heat shrinkable,oxygen barrier film having a food contact layer comprising a nitrogencontaining myoglobin blooming agent; wherein the container encloses thefood product in a reduced oxygen environment and at least a portion ofthe film food contact surface is in contact with at least a portion of asurface of the myoglobin-containing food product; wherein the myoglobinblooming agent is present on the food contact layer surface in aconcentration sufficient to produce a desirable surface coloration ofthe meat product and prevent undesirable extension of the color into thebody of the food product; wherein the concentration of myoglobinblooming agent is between 0.001 to 0.900 mg/in².
 27. A food package, asdefined in claim 26, wherein the myoglobin blooming agent is selectedfrom the group consisting of: Fremy's salt, nitrate salts having theformula (MNO₃) and nitrite salts (MNO₂), where M is a counter-ion (M+)selected from the group consisting of: alkali metals, alkaline earthmetals, transition metals, protonated primary, secondary, tertiaryamines, quaternary amines, and ammonium.
 28. The food package of claim26, wherein the food product is maintained in a vacuum.
 29. A foodpackage, as defined in claim 26, wherein at least a portion of the filmfood contact layer is transparent and in contact with the food product.30. A food package, as defined in claim 29, wherein the containerfurther comprises a tray.
 31. A food package, as defined in claim 30,wherein at least a portion of the food product is maintained in contactwith a modified atmosphere having an elevated level of carbon monoxide,nitrogen, an oxide of nitrogen, oxygen, or mixtures thereof.
 32. A foodpackage, as defined in claim 26, wherein the myoglobin blooming agent isnongaseous.
 33. A food package, as defined in claim 26, wherein the foodproduct comprises between about 0.1 and 25 mg/g myoglobin.
 34. A foodpackage, as defined in claim 26, wherein the food product comprisesbetween about 3 and 20 mg/g myoglobin.
 35. A food package, as defined inclaim 26, wherein the food product comprises between about 1 and 5 mg/gmyoglobin.
 36. A food package, as defined in claim 26, wherein the foodproduct comprises less than 1 mg/g myoglobin.
 37. A food package, asdefined in claim 26, wherein the food product comprises at least 1 mg/gmyoglobin.
 38. A food package, as defined in claim 26, wherein the foodproduct is selected from the group consisting of: beef, veal, pork,mutton, lamb, poultry, chicken, turkey, duck, goose, game, fish, andseafood.
 39. A food package, as defined in claim 26, wherein the foodproduct is primal, subprimal, retail cut, comminuted, ground, or acombination thereof.
 40. A food package, as defined in claim 26, whereinthe food product is fresh, frozen, hard chilled, or thawed.
 41. A foodpackage, as defined in claim 26, wherein the film has an oxygentransmission rate of less than about 310 cm³/m²/24 hours measured at 0%relative humidity and 23° C.
 42. A food package, as defined in claim 26,wherein the film has an oxygen transmission rate of less than about 20cm³/m²/24 hours measured at 0% relative humidity and 23° C.
 43. A foodpackage, as defined in claim 26, wherein the package comprises a pouch,bag, casing, overwrapped tray or form shrink package.
 44. A foodpackage, as defined in claim 26, wherein the package is hermeticallysealed.
 45. A food package, as defined in claim 26, wherein the foodcontact layer has a uniform distribution of myoglobin blooming agent onits surface.
 46. A food package, as defined in claim 26, wherein thefood contact layer comprises between about 0.1 weight % and about 5.0weight % of a myoglobin blooming agent incorporated therein.
 47. A foodpackage, as defined in claim 26, wherein the food contact layercomprises at least about 0.1 weight % of a myoglobin blooming agentincorporated therein.
 48. A food package, as defined in claim 26,wherein the food contact layer comprises less than 2.0 weight % of amyoglobin blooming agent incorporated therein.
 49. A food package, asdefined in claim 26, wherein the food contact layer comprises betweenabout 0.75 weight % and about 1.75 weight % of the myoglobin bloomingagent.
 50. A food package, as defined in claim 26, wherein the myoglobinblooming agent is present in an amount sufficient to cause the myoglobincontaining food product when hermetically sealed in a vacuum to have acolored food surface which at least 10 days after packaging is a visiblered hue.
 51. A food package, as defined in claim 26, wherein themyoglobin containing food product has a water content of at least 40 wt.%.
 52. A food package, as defined in claim 26, wherein the myoglobincontaining food product has a water content of at least 60 wt. %.
 53. Afood package, as defined in claim 26, wherein the myoglobin containingfood product has a sodium chloride content of less than 2.0 wt. %.
 54. Afood package, as defined in claim 26, wherein the myoglobin containingfood product has a sodium chloride content of 1.0 wt. % or less.
 55. Afood package, as defined in claim 26, wherein the myoglobin containingfood product has a combined nitrite and nitrate content of less than0.012 wt. %.
 56. A food package, as defined in claim 26, wherein themyoglobin containing food product has a combined nitrite and nitratecontent of less than 0.005 wt. %.
 57. A food package comprising: amyoglobin-containing food product having a water content of at least 5wt. %; and a container comprising a heat shrinkable, oxygen barrierthermoplastic film having a polymeric food contact layer and a tray;wherein the container encloses the food product in a reduced oxygenenvironment; and the food product is maintained in a modifiedatmosphere; wherein the film comprises a nitrogen containing myoglobinblooming agent; wherein the myoglobin blooming agent is present on thefood contact layer surface in a concentration sufficient to produce adesirable surface coloration of the meat product and prevent undesirableextension of the color into the body of the food product; wherein theconcentration of myoglobin blooming agent is between 0.001 to 0.900mg/in².